Republicans Eye 6 Seats to Win Control of Senate With Americans heading to voting booths today, control of the Senate hangs on one magic number: six. Republicans must flip at least half a dozen seats now held by Democrats and hold onto all of their own in order to seize control of the Senate. The battle for the Senate comes at a time when President Obama???s favorability has reached an all-time low, with only 44 percent of Americans saying they have a favorable view of him. Republicans have tried to turn the election into a referendum on Obama, tying him to their Democratic opponents in stump speeches and campaign ads. Here???s a look at the state of play in the key Senate races that will help determine control of the Senate, arranged by poll closing times. This story will be updated throughout the night to reflect race projections. Michelle Nunn is hoping to become the first Democrat to represent Georgia since the state???s wholesale Republican shift in 2002. Nunn, 47, a nonprofit administrator and daughter of a well-regarded former senator, has run as a moderate against Perdue, a cousin of a former governor who served as CEO of Reebok and Dollar General. He has touted his business experience on the trail, but has faced criticism for comments made in a leaked deposition when he said he had spent most of his career outsourcing jobs abroad. Since then, the race has tightened up, with neither candidate polling above the 50 percent needed to avoid a costly Jan. 6 runoff. Libertarian candidate Amanda Swafford could pull thousands of voters in her direction and send the race into overtime. Nunn will need strong African-American turnout to flip the seat held by retiring Republican Sen. Saxby Chambliss, and help Democrats defend their Senate majority. An NBC-Marist poll released last week found Perdue leading Nunn 48 to 44 percent, with Swafford acting as a potential spoiler at 3 percent. Senate Minority Leader Mitch McConnell has dreams of helming a GOP-controlled Senate, but he must win his re-election bid against Democrat Alison Lundergan Grimes before all else. Grimes, Kentucky???s 35-year-old secretary of state, has worked hard to run against McConnell???s 30-year history in Washington, but has lost steam in recent weeks after she refused to disclose whether she voted for President Obama. In one of the most expensive races in the country, McConnell has kept to the playbook of tying Grimes to Obama. "I think we're going to have a good day here in Kentucky and, hopefully, around the country," McConnell said after voting in Louisville. ???I'm hoping we're going to have a new majority to take America in a different direction.??? An NBC-Marist poll released last week found McConnell leading Grimes by 9 points. The race between Democratic Sen. Kay Hagan and Republican state House Speaker Thom Tillis is not only the season???s most costly - spending topped $100 million last week - but also one of the most bruising. Tillis has fought as hard as any Republican on the map to paint Hagan as a cipher for President Obama, and has criticized her for lacking leadership on national security and the response to ISIS. Hagan has harangued Tillis for the state???s recent rightward shift in Raleigh on budgetary and social issues, from education funding to the defunding of Planned Parenthood. Democrats have led early voting in North Carolina and are counting on African-American turnout to help Hagan defend her seat. Black and women voters make up a greater share of the early vote total than 2010. Sean Haugh, a pizza man and Libertarian candidate, could play the spoiler for Republicans with single-digit support. In 2008, Democrats took the state by just 14,000. A CNN-ORC poll released last week found Hagan leading Tillis 48 to 46 percent, with Haugh at 4 percent. Scott Brown, the former Massachusetts senator unseated by Sen. Elizabeth Warren in 2012, is looking to become the third senator in American history to represent two states with his bid for Democrat Jeanne Shaheen???s seat in New Hampshire. While facing criticism for being a ???carpetbagger,??? Brown has run an aggressive campaign against President Obama???s record on immigration, ISIS, Ebola and Obamacare, tying Shaheen to each policy along the way. Democrats are optimistic that Shaheen will hold her seat, but should Shaheen fall, it could represent a Republican wave in more competitive races. A WMUR-University of New Hampshire poll released Sunday had Shaheen leading Brown by 2 points. Two-term Sen. Mark Pryor is one of the country???s most vulnerable Democratic incumbents, facing a challenge from 37-year-old Rep. Tom Cotton, R-Ark. Pryor is part of a popular political lineage in Arkansas ??? his father, David, was a governor and senator from the state ??? and his family maintains close ties with Bill and Hillary Clinton. The former president even tried to give Pryor, the lone Democrat in the state???s congressional delegation, a boost by campaigning for him on multiple occasions in their home state. But Republicans hope Cotton, a former Army Ranger who served in Iraq and Afghanistan, will be able to switch the state???s seat. Throughout the campaign, Cotton has attempted to tie Pryor to President Obama, whose favorability rating has reached an all-time low. Meanwhile, Pryor has highlighted several of Cotton???s votes on the farm bill and disaster relief that might not fare well with Arkansas voters. An NBC News-Marist poll conducted in mid-October found Cotton leading Pryor among likely voters by 2 points. Months out from Election Day, it looked as if Democratic Sen. Mark Udall would coast to re-election in the state where Democrats revolutionized voter outreach with Sen. Michael Bennet???s campaign in 2010. But Republican Cory Gardner, a telegenic congressman and prized Republican recruit, began picking up steam in the Rocky Mountain State after he surprisingly entered the race in March. With his support for renewable energy and over-the-counter birth control, he has billed himself as an energetic new breed of Republican. He has managed to turn Udall???s attacks on his women???s health record into a liability for the incumbent and, surprisingly, nabbed the Denver Post???s endorsement along the way. Registered Republicans have a lead over Democrats in early ballot returns, but the Udall campaign is hoping the universal mail-in ballots will break in their favor, as will the Hispanic vote. A Quinnipiac poll released Monday found Gardner leading Udall with likely voters 45 percent to 43 percent. Sen. Mary Landrieu, D-La., finds herself in a three-way matchup in Louisiana as she tries to hold onto her Senate seat for a fourth term. Two Republicans are challenging Landrieu, who comes from a political family in Louisiana, this year: Rep. Bill Cassidy, R-La., and Rob Maness, a retired Air Force colonel. But the outcome of the Louisiana Senate race, and potentially the makeup of the Senate, likely won???t be determined on election night. The race is expected to head into a Dec. 6th runoff if one candidate doesn???t secure 50 percent of the vote. An NBC News-Marist poll released Sunday found Landrieu leading among likely voters with 44 percent of the voter. Cassidy and Maness lagged behind at 36 and 15 percent, respectively. Republicans originally thought the Kansas Senate seat would be safe, but a September shakeup threw the fate of the seat into question. Republican Sen. Pat Roberts, who has represented Kansas in Washington since 1981, is in a tight race against independent businessman Greg Orman, who received a major boost in the polls when Democrat Chad Taylor dropped out of the race in early September. Orman has declined to say which party he would caucus with should he win the Senate seat, but Republicans suspect he???d align himself with Democrats. If Roberts is unable to hang onto the seat, Kansas could be one of the few Republican incumbents to lose this cycle. After voting in Olathe, Kansas, Orman expressed optimism about the race, ???We feel really good about where we are and just hoping people go out and vote today. An NBC News-Marist poll released in October found Orman leading Roberts by 1 point. The race for the seat of retiring Democratic Sen. Tim Johnson picked up in October when the Democratic Senatorial Campaign Committee unexpectedly unveiled plans to spend $1 million on ads in the quiet four-way race headlined by Republican frontrunner Mike Rounds, Democratic candidate Rick Weiland and independent Larry Pressler, a former Republican senator. The move was an attempt to shake up the race enough for Weiland to pull off an upset over Rounds - a former governor - thanks to Pressler???s presence in the race. Republicans soon matched with a high-priced buy of their own, but both parties scaled back their initial moves when further polling showed Rounds in control. While the race may not be one of the most exciting on Election Night, it has been one of the most colorful: Pressler, who once considered running for mayor of Washington, D.C., has read poetry on the campaign trail, while Weiland has released a number of country-song covers as political ads. An NBC-Marist poll released in October found Rounds leading with 43 percent, ahead of Weiland at 29 percent and Pressler at 16 percent. The highly competitive Iowa Senate race has produced some of the most colorful moments of the campaign, from an ad about hog castration to a battle over roaming chickens. Republican candidate Joni Ernst and Democratic Rep. Bruce Braley are vying for the open seat in a state that launched President Obama to national stardom in 2008. Ernst, a little-known state senator and Iraq war veteran, shook up the Iowa Senate race with a provocative ad about castrating hogs. If Ernst ekes out a win, she would be the first female senator from Iowa and could also hold an influential role in the 2016 Iowa caucus. Braley has faced a few stumbles in his campaign, including comments that insulted some Iowa farmers and even having high-profiled surrogates forget his name. Senate Majority Leader Harry Reid has said control of the Senate hinges on the outcome of the Iowa Senate race. A Quinnipiac poll released Monday found Braley and Ernst locked in a dead heat, each polling at 47 percent. First elected to the Senate the same year as Barack Obama won the presidency, Democratic Sen. Mark Begich is fighting to secure a second term in the U.S. Senate. He???s opposed by Republican Dan Sullivan, the state???s former attorney general and a lieutenant colonel in the U.S. Marine Corps. Democrats are banking on their strong ground game in distant areas to help Begich keep his seat, but Republicans hope Sullivan???s efforts to link Begich to Obama will help him win another seat for the GOP. Over the weekend, Sen. Ted Cruz and former GOP presidential nominee Mitt Romney swooped into the state to help Sullivan shore up support among the conservative base. With polls closing at 1:00 a.m. ET and the need to count ballots from far-flung communities, results for the Alaska Senate race ??? and potentially control of the Senate - may not be known for days. There is little airworthy polling in the state, but an early October CNN poll found Sullivan leading Begich 50 to 44 percent.