The fight for control of the United States Senate is really close. It’s basically a coin-flip. Democrats have a 53 percent chance of winning a Senate majority according to FiveThirtyEight’s polls-plus model, or a 52 percent chance according to our polls-only forecast. There is about a 16 percent chance, in fact, that we’ll end up with a 50-50 Senate and the presidential race will decide control. (The vice-president breaks ties in the Senate.) 
 
 There are structural factors working in both parties’ favor. Republicans hold 24 of the 34 seats that are up for reelection in 2016. Democrats, therefore, have more opportunities to pick up seats than Republicans. The political geography also favors Democrats. Of the 10 seats Democrats are defending, none are in states that were won by either John McCain or Mitt Romney in 2008 or 2012. Republicans, by contrast, are defending a lot of turf that’s either blue or purple. That’s because the last time these seats were up for reelection was in 2010, a GOP-wave year when Republicans won a lot of seats in Democratic-leaning territory. In total, nine of the GOP-held seats up for grabs on Tuesday are in states that President Obama won in either 2008 or 2012. 
 
 On the other hand, Republicans are defending those seats — that is, they have more incumbents on the ballot. Incumbent candidates generally outperform non-incumbent candidates, all else being equal. And indeed, Republican incumbents are generally polling better than Donald Trump. 
 
 Speaking of the presidential race, one of the clearest trends this cycle has been that Democratic chances of taking back the Senate have generally run hand-in-hand with Hillary Clinton’s chances of winning the presidency. 
 
 The past few weeks have been no different. Democrats, who in the middle of October held a clear advantage in their fight for a Senate majority, have seen their fortunes fall as the presidential race has tightened. This matches a pattern seen over the previous few election cycles: More voters casting their ballot for the same party in both Senate and presidential races. There is some good news for Senate Democrats in this tightening, though: If voters think Clinton is less of a sure bet to win the presidency, they may be less likely to vote for Republicans in down-ballot races in order to act as a check on her power. That seemed like a possibility after Clinton opened up a large lead over Trump after the first debate in late September. 
 
 OK, so that’s the broad view of where things stand. Republicans currently hold 54 Senate seats. Democrats have 46 (including independents Angus King of Maine and Bernie Sanders of Vermont, who caucus with them). So Democrats need to pick up a net gain of four seats for a tie, or five seats to get an outright majority. 
 
 The FiveThirtyEight Senate forecast has 11 seats to watch. Let’s go through those 11 seats, from most likely to go Democratic to least likely, according to the polls-plus model. I’ve also added two extra wild-card races to keep an eye on as the returns come in Tuesday. 
 
 Likely Democratic pickup 
 
 Illinois (97 percent chance of a Democratic win in polls-plus forecast) 
 
 Republican Sen. Mark Kirk was always facing an uphill battle in solidly blue Illinois. Clinton is favored to win the state by more than 10 percentage points, and no Republican has won a Senate race in Illinois in a presidential election cycle since 1972. Kirk wasn’t helped when Democrats were able to recruit Rep. Tammy Duckworth, an Iraq-war veteran, to challenge him. Kirk has the voting profile (moderate) and geographic base (suburbs of Chicago) that a Republican needs to win a statewide race in Illinois, but even so he would have had to run an almost perfect campaign to have a chance. He hasn’t. He also had to fight off the belief among some voters that a stroke he suffered while in office has limited his effectiveness. If Kirk is to upset Duckworth, he’ll have to hold her margin in Cook County (Chicago) under 35 percentage points and lose pretty much no place else. 
 
 Probable Democratic pickup 
 
 Wisconsin (86 percent) 
 
 Wisconsin may be closer than our forecast suggests: Our model may not have fully picked up a late shift in the polls toward incumbent Republican Sen. Ron Johnson. Democrats were able to recruit former Sen. Russ Feingold to take on Johnson, and polls showed Feingold as the favorite for most of the year. Wisconsin hasn’t voted for a Republican for Senate in a presidential year since the Republican wave of 1980, and Johnson has a very conservative record. Johnson, though, appears to be mounting a comeback. Both Democratic and Republican groups have invested heavily in the race in the past few weeks. And Marquette University, perhaps the most reliable pollster in Wisconsin, put Johnson down just 1 percentage point in its final survey of the race. Other recent polls also point to a close contest. Feingold is still a favorite, and he will probably be helped by Clinton’s coattails — she holds a healthy lead over Trump in the state. But keep an eye on eye on the traditionally Republican-leaning counties outside of Milwaukee to see by how much Johnson is outperforming Trump. If it’s by a lot, as some polls suggest, Johnson has a shot. 
 
 Leaning Democratic 
 
 Pennsylvania (67 percent) 
 
 Yet another seat won by a Republican in a midterm election that will be harder to hold in presidential year. (Are you noticing a trend?) Republican Sen. Pat Toomey is one of the most conservative senators in Congress, despite representing a state that tends to vote Democratic in presidential elections. Beltway Democrats were able to get their preferred candidate, Katie McGinty, through a competitive primary, but the race between McGinty and Toomey was neck-and-neck through early October. Since then, however, McGinty has opened a small lead in almost every poll. Toomey has had his hands full with Trump, trying to keep his distance without outright disavowing the GOP nominee. McGinty, on the other hand, is probably going to be helped by Clinton, who is a favorite to win the state. Watch Chester County in the southeast part of the state. Chester County traditionally votes Republican, but Clinton is expected to overperform there. Toomey may need some ticket-splitting in that county to win the state. 
 
 Tossups 
 
 Missouri (44 percent), Nevada (56 percent), New Hampshire (52 percent) 
 
 These are the three seats where the Senate is most likely going to be decided. If Democrats win two of these three, it’s difficult to see how they don’t end up with at least 50 Senate seats. If they don’t, they’ll have to pick up at least one seat that appears to be trending away from them. 
 
 Missouri is perhaps the most interesting of the three because it’s the state where we have the best chance of seeing one party win the Senate race and the other win the presidential race. Although Trump should win easily in Missouri, Democrat Jason Kander has made the Senate race there quite competitive. Running on his biography as an Army veteran and outsider, Kander has fought his way to a near tie against Republican Sen. Roy Blunt. Blunt seems to have been caught flat footed, tagged as a Washington insider while his party’s presidential nominee runs against Washington. Still, Kander seems to have hit a wall in recent polls. Blunt has the slightest of edges in our forecast, but the race is really too close to call. One county to pay extra attention to is Jefferson County, near St. Louis, which has a history of matching the statewide vote. In 2012, the final margins in the gubernatorial, presidential and Senate races in Jefferson looked a lot like the state as a whole. 
 
 If turnout for Trump might help Blunt in Missouri, he’s likely to hurt Republican Joe Heck in Nevada. Heck is running against Democrat Catherine Cortez Masto to fill the seat of retiring Democratic Sen. Harry Reid. Heck, like Toomey in Pennsylvania, has struggled to figure out how exactly to deal with the Republican presidential nominee. While the polls point to a close race, the early vote in Nevada has been decidedly negative for Republicans. That doesn’t mean Heck is toast. Four years ago, Republican Sen. Dean Heller was able to win by 1 percentage point even as President Obama carried Nevada by 7 points. Heller, though, benefitted from a Democratic opponent who had ethics problems. Heck doesn’t have that luxury. Heck’s best chance is to win a larger share of Latinos than Trump in Clark County, where they are turning out in large numbers. 
 
 Unlike in Nevada, the recent trends have been good for Republicans in New Hampshire. Trump has closed the gap with Clinton there, and Republican Sen. Kelly Ayotte has made her race with Democratic Gov. Maggie Hassan a tossup again. There’s a touch of irony in Ayotte’s fate being tied to Trump’s; she has said she won’t vote him after facing backlash for calling him a good role model during a debate. The tight race shouldn’t come as a surprise: New Hampshire is the ultimate swing state. On the presidential level, it has been within a few percentage points of the national vote in every election since 1996. This year looks to be no different. With two well-known candidates running, the race looks like it will come down to the wire. The candidate who carries the independent vote in the state (which has one of the largest independent votes in the nation) will probably win the race. 
 
 Plausible Democratic pickups 
 
 Indiana (40 percent), North Carolina (30 percent) 
 
 Democrats thought they hit the jackpot when they were able to recruit former Indiana Sen. Evan Bayh into the race to replace retiring Republican Sen. Dan Coats. Bayh had been a two-term governor and senator. He also had a giant fundraising war-chest and opened the race with a large lead over Republican Todd Young. But that advantage has evaporated in the past few months. That’s not totally surprising given Trump is expected to easily carry the state. Bayh, though, hasn’t helped his cause. He’s been tied to Washington lobbyists and has been questioned on how much time he really spends in Indiana. Young, for his part, has improved his name recognition. The result is that Young took his first lead in a public poll in the last two weeks. Still, the race is close and could be won by either candidate. To win, Bayh will need strong turnout in heavily black Lake County (Gary) and Marion County (Indianapolis). 
 
 Democrats have a different problem in North Carolina. Republican Sen. Richard Burr had probably hoped the slight Republican tilt of the Tar Heel State would ensure his re-election, especially after the Democrats’ strongest potential candidate, Attorney General Roy Cooper, decided to run for governor instead. That left Democrats with Deborah Ross, a lawyer and former member of the North Carolina House of Representatives. Ross has kept it close with Burr the entire campaign, but she’s never been able to overtake him. That makes this race the only one examined so far in which the Democrat has never led in the FiveThirtyEight polls-plus forecast. There are very few swing voters in North Carolina, so the race is all about turnout: If Clinton outperforms expectations in the presidential race by just a few points, she might carry Ross across the finish line. 
 
 Longshot Democratic pickup 
 
 Florida (13 percent) 
 
 Democrats were a favorite to win the Senate seat in Florida until Republican Sen. Marco Rubio changed his mind and decided to run for reelection after all. Rubio has held a consistent lead over Democrat Patrick Murphy. Rubio has strong ties to Cuban communities in Florida, and he’s expected to vastly exceed Trump’s poll numbers among Hispanics in the Sunshine State. Keep an eye on heavily Cuban Miami-Dade County to see how much Rubio is outperforming Trump’s margins with Cubans. Murphy, for his part, has been called out for exaggerations about his record and has attacked Rubio for supporting Trump, even after Rubio called Trump a con artist in the presidential primary. For whatever reason, the attacks don’t seem to be sticking. Rubio’s advantage is so large at this point that it’s difficult to imagine Murphy winning even if Clinton wins the state. 
 
 Really long shot Democratic pickups 
 
 Arizona (3 percent), Ohio (2 percent) 
 
 Early polls indicated that incumbent Republican Sens. John McCain of Arizona and Rob Portman of Ohio might be in trouble. And Democrats recruited strong candidates: Ann Kirkpatrick in Arizona and former Gov. Ted Strickland in Ohio. But McCain and Portman have been perhaps more successful than any other Republican Senate candidates in distancing themselves from Trump. Portman was also helped by a massive fundraising advantage over Strickland. 
 
 Wild cards 
 
 Colorado (95 percent), Louisiana (14 percent) 
 
 No one has talked about Colorado as a potential Republican pickup. Democratic Sen. Michael Bennet has only trailed in one poll all year against Republican Darryl Glenn. Colorado, though, is still a swing state in presidential elections, even if Clinton is favored to win it this year. It also elected a Republican to the Senate in 2014. And Bennet’s lead in the polls has shrunk to within single digits over the past month. Bennet will almost certainly still win, but don’t be surprised if the race ends up closer than many once thought it would be. 
 
 Louisiana is something entirely different. The state will hold on a primary on Tuesday in which all the Democratic candidates and Republican candidates run against each other. As long as no candidate gets 50 percent (and there’s basically no chance of that happening), the two top vote getters regardless of party affiliation will advance to a runoff. It’s expected that one of those candidates will be Republican John Kennedy who leads in the polls. But Democrats Foster Campbell and Caroline Fayard are not too far behind Kennedy in second and third respectively. With five Republicans projected to get at least 4 percent of the vote, it’s possible that Republicans will split their vote enough that Kennedy drops to third and both Democrats end up advancing. Keep in mind that polls are much more likely to be wrong in primaries than in general elections. 
 
 It is possible that one party will win most of the battleground races. The polls are sometimes off in the same direction in multiple races. That happened in 2014 when Republicans beat their polls across the board. If that happens again, then some of the long-shot candidates may end up as surprise winners. 
 
 Still, the polls show a close overall race — about as close as you can get. In nearly half of our simulations, the Senate ends up as either tied or 51-49 in one direction or the other. So as you watch the presidential race unfold, remember that it’s not just determining control of one branch of government but potentially half of another branch as well. ||||| As the final, frantic hours of the campaign for control of Congress come to a close, Democrats look like slightly-better-than-even favorites to reclaim the Senate, while Republicans appear certain to hold the House after a Donald Trump-induced October scare. 
 
 If Democrats manage to flip the Senate, senior party aides and strategists involved in battleground races said they’re looking at a majority of 52 seats, best case. That would be a letdown from their earlier hopes of a 54- or 55-seat advantage and put Republicans in the pole position to win back the chamber in 2018. 
 
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 Senate Republicans are conceding nothing, though. The conservative Senate Leadership Fund has poured a jaw-dropping $37 million into the most competitive races over the past two weeks. Republican hopefuls are outperforming Trump and could conceivably prevail in enough of the half-dozen top contests to prevent a Democratic takeover. 
 
 “We are going to keep the majority,” declared Arkansas Sen. Tom Cotton, a vice chairman of the National Republican Senatorial Committee who has barnstormed the country this fall to campaign for GOP lawmakers. “I don’t think the presidential race will be a major factor … [voters] distinguish between the presidential race on the one hand … and the Senate races.” 
 
 Democrats’ confidence is rooted in Hillary Clinton’s narrow edge in national polls, which they believe offsets a late-game injection of uncertainty courtesy of FBI Director James Comey. Democrats need to pick up four seats if Clinton wins, and five if Trump prevails. 
 
 “I have a little heartburn over what Comey did. I think it was bizarre; I wouldn't have ever expected that in a million years,” Sen. Claire McCaskill (D-Mo.) said in an interview. But “I just don't see how [Trump] could ever pull this off. And I also feel pretty good about the Senate races.” (The interview occurred before Comey announced Sunday that he's standing by his conclusion that Clinton should not be prosecuted for her handling of classified material.) 
 
 On the House side, meanwhile, most political insiders agree it’s likely to remain safely in Republican hands as the threat of an anti-Trump wave has dissipated. House Republicans privately assert that a number of GOP incumbents once considered to be most at risk of losing — including John Katko and Lee Zeldin of New York, Carlos Curbelo of Florida and Mike Coffman of Colorado — are leading their Democratic challengers. 
 
 Hill Republicans are hoping to keep their losses to under a dozen seats. 
 
 “I feel like we’re in the best shape we could possibly be in, given that it’s a presidential election cycle,” Rep. Steve Stivers (R-Ohio), a deputy chairman of the National Republican Congressional Committee who’s expected to take over the organization next year, said in an interview. “I am certain Democrats will not take back the House; it’s not even a possibility.” 
 
 It’s surprising that the race for the Senate is as close as it is, given that Republicans are defending 24 seats, many in blue and purple states, and running with the bombastic Trump atop their ticket. Ironically, they have Trump to thank: As he recovered slightly in the polls the past two weeks, so did Republicans’ dwindling chances of keeping the Senate. 
 
 The New York Times’ Upshot model has Democrats’ chances of winning the chamber at 53 percent, while Nate Silver's FiveThirtyEight says it’s 50-50. Charlie Cook told NBC's Chuck Todd over the weekend he believes Democrats will pick up at least four seats. 
 
 GOP senators are pulling out all the stops to cut through the noise in the presidential race. Sen. Kelly Ayotte (R-N.H.) is aiming to make 50 campaign stops in five days, capped by a 24-hour sprint. Sen. Pat Toomey (R-Pa.) is spending the last days of the race sparring with President Barack Obama after running an ad showing the president praising Toomey’s work on gun control. And Sen. Ron Johnson (R-Wis.) spent the weekend with House Speaker Paul Ryan (R-Wis.) on a tour of a state where GOP skepticism of Trump runs deep. 
 
 As many as eight Senate races could go either way. Illinois is the lone safe pickup for Senate Democrats. But sources in both parties privately admit that Democrats are favored to take back the majority given the sheer number of GOP-held states in play. 
 
 Democrats believe that Johnson will fall short in his comeback bid, though they are fretting about former Sen. Evan Bayh (D-Ind.), whose lead in Indiana has evaporated. Republicans wish they had a few more days to prosecute their case against Bayh in what is being cast as a bellwether race. 
 
 “If a Democrat wins there, it’s probably a sign that they’re going to get a big number of seats,” Amy Walter of the Cook Political Report said Sunday on “Face the Nation.” 
 
 Some states are moving Democrats’ way at the last moment. A surge of Latino early voters in Nevada “probably” will lift Democrat Catherine Cortez Masto over Rep. Joe Heck (R-Nev.) in the only state where Republicans are on offense, Nevada political writer Jon Ralston concluded over the weekend. And 10 of the past 12 RealClearPolitics polls give Katie McGinty a lead over Republican incumbent Toomey in Pennsylvania, where Republicans say Toomey’s strong campaign may be swamped by Democrats’ million-voter registration advantage. 
 
 New Hampshire’s race, between Sen. Kelly Ayotte and Democratic Gov. Maggie Hassan, is viewed as the purest toss-up. 
 
 “In a small state with lots of polls in the field simultaneously and voters' phones ringing off the hook, it's difficult to get a representative sample,” said Aaron Jacobs, a spokesman for Hassan, after a rash of polls narrowly favored Ayotte. 
 
 Two conservative states are moving different ways, according to internal party assessments. Republicans have little confidence in Sen. Roy Blunt (R-Mo.) pulling it out against young and charismatic Democratic hopeful Jason Kander. 
 
 But Democrats seem less bullish about knocking off Sen. Richard Burr (R-N.C.) than they were two weeks ago. 
 
 Burr's hopes appear directly tied to Trump’s performance in his home state, a must-win for Republicans to take the presidency. 
 
 “There’s no question that Donald Trump has had an enormous amount of momentum. And it’s helping his chances and the senators out there that are running,” Republican National Committee Chairman Reince Priebus said Sunday on ABC’s “This Week.” 
 
 Though Florida is competitive, Republicans are confident that Sen. Marco Rubio’s universal name ID and big money advantage will prevail. But keeping the majority will essentially require Republicans to run the table elsewhere. 
 
 Control of the Senate will be critical for the next administration to confirm its nominees. And the slimmer the House majority next year, the tougher it will be for Ryan to govern the House Republican Conference. 
 
 The conference could lose up to three senior Republicans. Rep. Scott Garrett’s (R-N.J.) refusal to support gay Republican candidates is costing him in his New Jersey district outside New York City. And Republicans are nervous about longtime Reps. John Mica (R-Fla.) and Darrell Issa (R-Calif.). 
 
 Seung Min Kim contributed to this report. ||||| McCain debates Kirkpatrick on Oct. 10 in Phoenix. (Ross D. Franklin/AP) 
 
 Arizona 
 
 Sen. John McCain (R) is poised to win a sixth term after a tough two-front battle with his state’s far-right wing and Democrats accusing him of flipping his positions to fit the moment. 
 
 McCain, 80, first had to get through a primary against Kelli Ward, who ran as a tea party insurgent proudly backing Donald Trump and aped Trump’s criticism of McCain over veterans’ legislation. McCain won comfortably, but received a tad more than 50 percent of the GOP vote. 
 
 That set up a quick and potentially difficult general-election battle against Rep. Ann Kirkpatrick (D), who represents the state’s largest district. But McCain quickly galvanized most of the Republican vote, running as a check against a possible Hillary Clinton presidency and trying to steer clear of discussing Trump. 
 
 Kirkpatrick has aired tough ads showing McCain’s changing positions, including in 2010 calling for a “danged fence” along the Mexican border. But Washington Democrats took a pass on engaging the race. Both the Democratic Senatorial Campaign Committee and its super PAC ally, Majority PAC, have not devoted resources to the race. 
 
 McCain formally dumped Trump in early October. A CNN poll showed him with a 13-point edge in the past week. 
 
 — Paul Kane 
 
 
 
 Harris gives a thumbs up to supporters during her visit to the campaign office of Rep. Ami Bera in Elk Grove, Calif., on Nov. 3. (Rich Pedroncelli/AP) 
 
 California 
 
 When Sen. Barbara Boxer (D) announced her retirement, California Attorney General Kamala Harris became the instant front-runner. Other Democrats stepped back, and no strong Republicans came forward in the deep-blue state. 
 
 Enter Rep. Loretta Sanchez (D). Sanchez made it through the June primary, defeating several GOP candidates to finish a distant second to Harris. State election rules allow the top two finishers, regardless of party, to advance to the general election. But the Orange County congresswoman has struggled to catch up to Harris, who in recent polls was leading by more than 20 points. 
 
 Sanchez has campaigned as a moderate and she’d hoped to mobilize Latinos, California’s largest ethnic group. She has modest leads with Latino voters in polls, but Harris boasts double-digit margins with nearly every other demographic group. 
 
 Harris has the backing of the California Democratic Party, labor unions and progressive groups, and President Obama, who appeared in a campaign ad for her. 
 
 Sanchez, 56, would be the first Latina elected to the Senate. Harris, 52, whose parents emigrated from Jamaica and India, would become the second black woman elected to the Senate since 1992. 
 
 — Vanessa Williams 
 
 
 
 Rubio, right, and Murphy debate on Oct. 26 at Broward College in Davie, Fla. (Wilfredo Lee/AP) 
 
 Florida 
 
 The most important day in Florida’s Senate race was June 22, when GOP Sen. Marco Rubio announced that he would seek reelection — reversing a pledge he made when he began his ill-fated presidential campaign. Without Rubio, Republicans faced a messy primary featuring several unknown, untested candidates. Democrats, meanwhile, thought they had a winner in Rep. Patrick Murphy, a young up-and-comer who had triumphed in the nastiest and most expensive House race of 2012. Rubio’s reversal instantly gave the GOP an advantage, and they have not given it up. 
 
 Rubio and GOP allies have spent tens of millions of dollars attacking Murphy, trying to paint him as a spoiled rich kid with a questionable professional record. Murphy has fought back with ads capitalizing on Rubio’s presidential ambitions and his poor Senate attendance record while pursuing them. But Democrats pulled millions of dollars of ad reservations over the course of the fall as other races proved to be more competitive, leaving Murphy unable to match Rubio dollar for dollar. 
 
 Murphy hasn’t caught up in polling, but he’s not far behind. A late influx of Democratic spending and a stronger-than-expected Clinton win could spell an upset — and a devastating loss for Rubio. 
 
 — Mike DeBonis 
 
 
 
 Kirk, right, and Duckworth debate on Oct. 27 at the University of Illinois in Springfield. (Seth Perlman/AP) 
 
 Illinois 
 
 Sen. Mark Kirk (R) has used a wheelchair since he had a stroke in 2012, and against virtually any other opponent, his return to the Senate would be a powerful narrative on which to run. 
 
 But his Democratic opponent, Rep. Tammy Duckworth, has a story just as powerful, having lost her legs in 2004 when her helicopter in Iraq was struck by an enemy rocket. It was during her recuperation that her home state’s two Democratic senators — Richard J. Durbin and Barack Obama — drafted her into politics. She has run a cautious but competent campaign withstanding attacks on her tenure as head of the state Department of Veterans Affairs and on her thin legislative record. 
 
 For Kirk, meanwhile, reelection was a tough bet, as Illinois last elected a Republican senator in a presidential year in 1972. And Kirk is his own worst enemy, talking his way into controversies that culminated in the most stunning congressional debate gaffe of 2016. 
 
 After Duckworth described her family’s military heritage, Kirk said he had “forgotten that your parents came all the way from Thailand to serve George Washington.” Although Duckworth’s mother is a Thai immigrant, her late father’s lineage can be traced to the Revolution. 
 
 — Mike DeBonis 
 
 
 
 Bayh participates in debate for Indiana's open U.S. Senate seat in Indianapolis on Oct. 18. (Michael Conroy/AP) 
 
 Young participates in debate for Indiana's open U.S. Senate seat in Indianapolis on Oct. 18. (Michael Conroy/AP) 
 
 Indiana 
 
 Everything changed in Indiana’s Senate race when former senator Evan Bayh (D) announced on July 11 that he would be running to retake his seat. Until that day, Republicans were convinced that Rep. Todd C. Young (R) had an easy path to victory. Bayh entered the race with strong support from Democrats, who have fond memories of his time as governor and senator. 
 
 But Bayh proved ill-prepared for a punishing Senate contest and has been pummeled by accusations that he is a Washington insider who is out of touch with Hoosiers. First, he incorrectly listed the address of his Indianapolis condominium, then he battled reports that he spent the final days of his last Senate term interviewing for high-paying jobs. 
 
 A poll conducted Oct. 22 to Nov. 3 by WTHR-TV and Howey Politics shows Bayh trailing by five points. 
 
 Young, who served as a Marine, has made a name in the state as fresh-faced alternative to Bayh’s storied career. His campaign has benefited from a flood of outside support from groups such as the U.S. Chamber of Commerce and the Senate Leadership Fund, the Karl Rove-backed super PAC run by former aides to Senate Majority Leader Mitch McConnell (R-Ky.). 
 
 — Kelsey Snell 
 
 
 
 Kander speaks to supporters at a St. Louis union hall on Nov. 1. (Jim Salter/AP) 
 
 Blunt, left, and his wife, Abigail, campaigns in Missouri on Oct. 8. (David Weigel/The Washington Post) 
 
 Missouri 
 
 Many Republican and Democratic operatives agree: No Senate challenger has run a better race than Jason Kander (D), Missouri’s secretary of state. It was a viral TV ad that had Kander assembling a military-style rifle with a blindfold that caught Washington’s eye, but it’s months of disciplined, pitch-perfect campaigning that puts him within a hair of unseating Roy Blunt (R) in a state likely to favor Donald Trump by double digits. 
 
 Kander, who was an Army intelligence officer, has leaned heavily on his military background and has found a receptive audience for his attacks on Blunt as a Washington insider. 
 
 Republican groups have been forced to come to Blunt’s rescue, financing ads linking Kander to Hillary Clinton and President Obama — some of them showing Kander’s face morphing into theirs. 
 
 Kander, meanwhile, has not passed up an opportunity to remind voters that Blunt lives in a D.C. mansion and that his wife and three of his children are lobbyists. And although Blunt has not distanced himself from Trump, he fits the profile of the D.C. denizen Trump is running against. Virtually every independent poll since September has shown a tied race or Blunt leading within the margin of error. 
 
 — Mike DeBonis 
 
 
 
 Cortez Masto shakes hands with Heck after an Oct. 14 debate in North Las Vegas. (Erik Verduzco/AP) 
 
 Nevada 
 
 Senate Minority Leader Harry M. Reid’s retirement announcement rocked Nevada’s political scene, creating the GOP’s only chance to capture a Democratic seat on the Senate battleground. 
 
 The race pits Rep. Joe Heck (R), who represents the Las Vegas suburbs, against former state attorney general Catherine Cortez Masto (D), who would be the first Latina senator. The state is difficult to poll, both because of its new Hispanic population and because employees working in the Las Vegas gambling and nightlife industry are hard to reach. 
 
 Divergent polls show Heck leading by about seven points, or Cortez Masto ahead by the same margin. Neither candidate has broken through policy-wise, nor has either’s personality crashed through the din of commercials here. 
 
 Much of Heck’s campaign isn’t focused on his rival but instead on Reid — casting him as a villain who chose his puppet to succeed him. And Cortez Masto’s is focused on Donald Trump, trying to energize Hispanics and mocking Heck’s wavering support for the GOP nominee. 
 
 The race may be decided in “the rurals,” counties far away from the Las Vegas Strip where Trump is expected to do well. Heck has withdrawn his support for Trump and called for him to quit the race, which may be why he is underperforming there. 
 
 — Paul Kane 
 
 
 
 Ayotte, left, and Hassan during a Nov. 2 debate. (Jim Cole/AP) 
 
 New Hampshire 
 
 For months, polls in New Hampshire have shown Sen. Kelly Ayotte (R) in a near dead heat with Gov. Maggie Hassan (D). The latest Boston Globe poll, conducted at the end of October, showed Ayotte leading by 2.5 points, well within the margin of error. 
 
 The outcome of the closely watched race is expected to play a critical role in determining which party will hold the Senate majority next year. 
 
 Ayotte, a former state attorney general, has struggled to overcome a powerful downdraft created by the unpopularity of Donald Trump. She sank in the polls when struggling to respond to a leaked 2005 recording of Trump talking about kissing women and grabbing them without their consent — at first standing by Trump and eventually rescinding her support. 
 
 Hassan has benefited from running as a well-liked sitting governor but she has struggled to eke out a consistent lead. Hassan had to overcome her own gaffe when she struggled to answer whether she thinks Hillary Clinton is honest and trustworthy. 
 
 The race has attracted more than $89 million in spending from outside groups, making it the second most expensive Senate contest this year, according to the Center for Responsive Politics. 
 
 — Kelsey Snell 
 
 
 
 Strickland greets a poll worker before voting at the Franklin County Board of Elections on Oct. 27. (Jay Laprete/AP) 
 
 Portman tours Pioneer Pipe while campaigning in Marietta, Ohio, on Oct. 25. (Spencer Platt/Getty Images) 
 
 Ohio 
 
 Sen. Rob Portman (R) was originally expected to be fighting for his political life in the campaign’s final days. 
 
 A consummate insider, having worked in both Bush administrations and as part of the House GOP leadership, he seemed ill-suited for the anti-Washington environment epitomizing this cycle. 
 
 But Portman seems to have prevailed after running what was probably the best race of any Republican candidate this year. He raised more money than all but one Senate Republican (Patrick J. Toomey, who is in a close contest), and spent it early and often, a smart tactic in hindsight. 
 
 His ads reintroducing voters to their first-term senator were effective, portraying his work to fight an opioid crisis with Senate legislation and to combat sex trafficking. Meanwhile, Portman’s negative ads battered Ted Strickland, who began the race as a well-liked former governor. But after being reminded of the job losses during Strickland’s term, voters had turned against the ex-governor by late August. National Democrats abandoned the race. 
 
 Of the 10 most recent public polls, all in October, Portman had a lead of at least 11 points. GOP strategists are already studying this campaign as a blueprint for future Republican Senate races. 
 
 — Paul Kane 
 
 
 
 Burr and Ross in a debate on Oct. 13. (Gerry Broome/AP) 
 
 North Carolina 
 
 Sen. Richard Burr (R) cuts an increasingly rare figure on Capitol Hill, a low-octane throwback to a time when the soul of the GOP was country-club conservatism, not sharp-edged populism. He has the old-school campaign ethos to match. 
 
 National Republicans fumed as he stuck with the winning formula from his previous two runs: Keep your powder dry until October, then hold on for dear life at the end. His opponent is Deborah Ross, a lawyer and former state lawmaker whose record as a civil-rights advocate many assumed would be too liberal for the state. 
 
 But Ross has proven a masterful fundraiser and fierce campaigner, and an avalanche of ads highlighting her past objections to the state’s sex-offender registry seem not to have deeply affected voters. Polls have shown a tight race for months, and although Burr has had a small lead in most recent polls, he has not been able to run far ahead of Donald Trump in a state where Democrats are making an extra-hard turnout push. 
 
 The final week was roiled when Burr was recorded in a private meeting cracking a joke about gun owners putting a “bullseye” on Hillary Clinton. Ross, meanwhile, has benefited from a pair of presidential visits. 
 
 — Mike DeBonis 
 
 
 
 McGinty and Toomey at a debate at Temple University in Philadelphia on Oct. 24. (Matt Rourke/AP) 
 
 Pennsylvania 
 
 The most expensive Senate race in history is in Pennsylvania, topping $140 million by late October, according to the Philadelphia Inquirer. 
 
 The money reflects the stakes of this contest. Democrats always believed their path to the majority probably required knocking off Sen. Patrick J. Toomey (R). Toomey tells supporters everywhere that their votes will keep the Senate in Republican hands. 
 
 Sen. Charles E. Schumer (N.Y.), the incoming Democratic leader, recruited neophyte Katie McGinty, persuading Vice President Biden to coax President Obama to endorse her in the primary. 
 
 Toomey and McGinty are basically deadlocked. McGinty has held a small lead in the past few polls — but over the past month, four showed the race tied and four gave Toomey a slight lead. 
 
 Toomey is performing well in the vote-rich Philadelphia suburbs. But he is doing less so in the rural stretch between Philadelphia and Pittsburgh, in part, strategists say, because he hasn’t said whom he supports for president. That may work near Philadelphia, where Hillary Clinton is crushing Donald Trump, but Trump is well-liked elsewhere. 
 
 Whichever party wins this race will have the edge to win the majority. 
 
 — Paul Kane 
 
 
 
 Johnson, left, and Feingold, right, meet in their second and final debate Oct. 18 in Milwaukee. (Mark Hoffman/AP) 
 
 Wisconsin 
 
 For months, Democrats considered Wisconsin a near-certain pickup. It has been a reliably blue state in presidential years, one-term incumbent Ron Johnson (R) had not done much to raise his profile and well-known former senator Russell Feingold (D) had signed up for a rematch. 
 
 Summer polls showed Feingold with a double-digit lead, but the well-respected Marquette Law School Poll found last week that that margin had shrunk to a single point amid a late GOP ad blitz. 
 
 In the final week of the campaign, about $6 million was spent by campaigns, party committees, super PACs and outside groups — many of which had canceled earlier reservations. 
 
 Johnson, an Oshkosh plastics manufacturer, has sought to refresh his image as a no-nonsense outsider businessman, while casting Feingold as a career politician and a throwback. Feingold, meanwhile, has relentlessly driven a middle-class economic message focused on opposition to trade deals and tax loopholes, while tarring Johnson as an advocate for corporate interests. 
 
 Although the race has tightened, Democrats and some Republicans think Feingold has an edge: Early voting has outpaced expectations in Democratic strongholds, and Johnson is only now showing signs of outpacing Donald Trump. 
 
 — Mike DeBonis
– So which party will control the Senate next year? Flip a coin. That's the current assessment at FiveThirtyEight.com, which gives Democrats a 52% or 53% chance of regaining control and a 16% chance of a 50-50 tie. In the latter case, the new VP would cast tie-breaking votes. Not too long ago, most forecasts comfortably predicted that Democrats would wrest control, but things have tightened considerably. The GOP currently has a 54-46 advantage (two independents caucus with Democrats), but Democrats have an opportunity to pick up ground up because 24 of the 34 seats up for grabs are held by Republicans. Some key races, per FiveThirtyEight, the Washington Post, and NBC News: New Hampshire: GOP Sen. Kelly Ayotte has been in a virtual dead heat with Democratic Gov. Maggie Hassan. This race in particular "is expected to play a critical role in determining which party will hold the Senate majority next year," notes the Post. Wisconsin: Republican Ron Johnson is defending his seat in a tight race against a familiar Democratic name, former Sen. Russ Feingold. Pennsylvania: Incumbent Republican Pat Toomey, a staunch conservative, is in a close one with challenger Katie McGinty, who could get a boost if Hillary Clinton wins the state. Illinois: GOP incumbent Mark Kirk is in real danger of losing to Democratic Rep. Tammy Duckworth. (Moments like this haven't helped him.) Missouri: Democratic challenger Jason Kander has a chance of ousting Republican incumbent Roy Blunt. Nevada: Harry Reid is retiring, and Republicans hope to get a flip of their own. The GOP's Joe Heck is keeping it close with Democrat Catherine Cortez Masto.