The once-collegial relationship between Harry Reid and Mitch McConnell has collapsed into a free-for-all of name-calling, finger-pointing and mutual mistrust. 
 
 The enmity manifested itself in a private confrontation on the Senate floor last month in which McConnell needled Reid over a super PAC — run by the Senate majority leader’s former aides — that attacked the GOP leader over the Kentucky airwaves. 
 
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 “I see your super PAC is up in Kentucky,” McConnell told Reid, according to two sources familiar with the exchange. “Come on down, I hope you spend it all down there.” 
 
 Reid’s curt response: I know nothing about super PACs. And the conversation was over. 
 
 The tension is growing as McConnell emerges as one of the Democrats’ top targets in 2014 and as the two men collide over an unprecedented change to Senate filibuster rules. The ill will and bitter feelings have never been more intense nor meant more to the Senate, according to close confidants of the two party leaders. 
 
 (PHOTOS: Mitch McConnell and Harry Reid's friendship) 
 
 The leaders are clashing because each believes the other is destroying the integrity of the institution, where they have spent nearly 60 collective years and taken similar paths to power. 
 
 If Reid deploys the “nuclear option” as early as Tuesday — in which senators would change the filibuster rules by a simple majority instead of 67 votes — gridlock in the Senate could worsen with major budget fights ahead in the fall and a slew of presidential nominees expected to hit the Senate floor in the coming months. 
 
 The rules change wouldn’t affect legislation or judicial nominees, but the nuclear option could be repeated by future majorities to further weaken the filibuster. 
 
 (Also on POLITICO: Reid digs in as Senate nears nuclear option showdown) 
 
 Since Reid and McConnell began serving together as opposing leaders six years ago, they’ve repeatedly claimed to have a productive and cordial working relationship, despite frequent clashes on the Senate floor. Because of the Senate’s peculiar rules, the two leaders must cooperate in order to get even the most routine business done. 
 
 But in recent months, their relationship has broken down over a sheer lack of trust, stemming from McConnell’s suspicion of Reid’s involvement in his 2014 campaign and intensifying as the Nevada Democrat has threatened to change filibuster rules despite McConnell’s furious objections. 
 
 McConnell believes Reid is breaching protocol between Senate leaders by getting directly involved in his reelection bid, while Reid thinks McConnell is simply using the spat to bolster his own reelection chances by running against Washington Democrats. 
 
 Last Thursday marked the most direct and open personal attacks between the two party bosses. Speaking off the cuff, a furious McConnell warned Reid would go down as the “worst” Senate leader “ever” if he changed filibuster rules by a straight majority vote. 
 
 But it was something else that infuriated Reid and his top aides — McConnell’s campaign team later tweeted out a cartoon with a picture of a Reid tombstone bearing the words “Killed the Senate” on it. Reid was taken aback. 
 
 “What is sad is how Sen. McConnell has decided to personalize this for his reelection purposes,” said David Krone, the majority leader’s chief of staff. “They obviously disagree on many issues, but I have never heard Sen. Reid speak so personally ill about Sen. McConnell in the fashion that Sen. McConnell has towards Sen. Reid.” 
 
 A McConnell spokesman fired back. 
 
 “If there’s anyone who’s making this a campaign issue in Kentucky, it’s Sen. Reid,” the spokesman said. “He recruited Sen. McConnell’s opponent, and his super PAC is demonizing the leader as an obstructionist with a quarter-million-dollar ad buy in Kentucky. Sen. Reid has manufactured an issue and is the one that’s making it a campaign issue in Kentucky.” 
 
 From McConnell’s perspective, both he and Reid have long been on the same page when it comes to protecting the Senate’s traditions, which have grown more important with the death of fierce institutional defenders like Robert Byrd. During the past two years, Reid had headed off a push by more junior Democrats to dramatically weaken the filibuster, opting instead to cut bipartisan deals with McConnell without invoking the nuclear option. But now, McConnell believes, Reid has gone back on his word. 
 
 Indeed, when news leaked that Reid was considering changing the filibuster rules, McConnell confronted Reid about his plans. In a private exchange, McConnell asked Reid directly if he would use the nuclear option, according to two sources familiar with the matter. 
 
 Reid wouldn’t tell McConnell what he would do, sources say, marking a bit of a role reversal. In private conversations, Reid has long had the habit of fully laying out his line of thinking to McConnell, while the GOP leader often keeps his cards close to his vest, according to insiders privy to those talks. 
 
 But this time, Reid wouldn’t say what he planned, angering McConnell. ||||| The theatrics reached a new crescendo Thursday when Majority Leader Harry M. Reid (D-Nev.) and Minority Leader Mitch McConnell (R-Ky.) confronted each other over Reid’s effort to change the filibuster rules in ways that would strip the GOP’s ability to block confirmation of executive branch nominees and that could ultimately weaken the minority party’s ability to slow the majority agenda. 
 
 Reid’s move provoked some of the most personal attacks two Senate leaders have leveled against another in decades; Reid described McConnell as untrustworthy, while McConnell countered that the Nevada Democrat would go down in history as the worst Senate leader ever. 
 
 Suddenly, the world’s greatest deliberative body just isn’t that much fun anymore. 
 
 “I miss it like an abscessed tooth,” former senator Christopher S. Bond (R-Mo.), a 24-year veteran, said on a recent visit to the Capitol. 
 
 The dysfunction fever is so strong that Reid and McConnell relented to a rank-and-file request to set up a rare meeting for senators of both parties Monday night in the Old Senate Chamber. 
 
 Those working at the last-gasp filibuster compromise fear that if they fail, the Senate will put itself on a permanent downward spiral later this week. 
 
 “There’s no doubt that it’s harder and it’s more partisan,” said Sen. John McCain (R-Ariz.), who has spent the past few days talking with senators and White House allies hoping to hatch a compromise on Senate rules. McCain has succeeded twice before at reaching a compromise to avoid partisan rule changes, first in 2005 and again this year. 
 
 “Each time we come closer and closer to having this happen,” McCain said Friday. 
 
 Interviews with more than a dozen current and recently retired senators paint a mostly dismal picture of life in the Senate. There is a growing sense of despair among the rank-and-file senators, who privately grouse that the two leaders, despite many similarities in style and background, have become so distrustful of one another they barely speak to each other, except for small talk about their shared love of the Washington Nationals. 
 
 One GOP senator last week pleaded with McConnell to reach out to Reid to establish some regular channel of communication, maybe a biweekly breakfast, to try to solve their problems. McConnell declined, saying he simply could not trust Reid, according to the Senate Republican, who asked for anonymity to speak about the relationship. ||||| Senate Majority Leader Harry Reid and Minority Leader Mitch McConnell are closing in on a deal that would avert the “nuclear option” on the filibuster but would pare back its use in several instances, sources said Wednesday. 
 
 No deal is final, sources said, but a bipartisan accord to avert a messy partisan showdown could be announced as soon as Thursday. 
 
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 The exact contents of the package remain murky, but Reid is expected to win GOP concessions to speed debate during a handful of occasions, including to end filibusters intended to prevent debate from beginning on bills. 
 
 Reid (D-Nev.) has been pushing McConnell (R-Ky.) to drop the amount of procedural votes needed to enter a conference with the House, something the two men appear close to agreeing on. Reid has also been demanding that senators stop the practice of extending debate for 30 hours once a Senate filibuster has been defeated. And he’s called for expedited consideration of certain presidential nominations. 
 
 In the private talks, McConnell has sought to ensure Republicans get at least two amendments on bills during floor debates, sources say. And Reid appears poised to grant the request, sources say. 
 
 Reid appears to have made some concessions. He had proposed to require senators mounting a filibuster to come up with the 41 votes to do so. Current rules require those trying to defeat a filibuster to find 60 votes. Reid appears to have dropped that proposal in his talks with McConnell, sources say. 
 
 And Reid has already dropped the so-called “talking filibuster,” a plan sought by liberals in his caucus and that would require senators to carry out a stalling session on the floor, rather than threaten them. Critics in both parties worried that it would virtually eliminate the filibuster. 
 
 A deal with McConnell would prevent Reid from taking the precedent-setting move of changing the rules by 51 votes, rather than 67, a move critics dub the “nuclear option” but supporters call the “constitutional option.” Future majorities could cite the precedent to change whatever rules they want, critics fear, eroding the power of the minority. 
 
 But Reid has grown furious at what he sees as GOP obstruction, and McConnell has demanded that the majority leader allow the GOP more opportunities to amend legislation. 
 
 A deal would still allow the GOP to filibuster in a number of other situations, including to end debate and prevent an up-or-down vote. And 60 votes would still be needed to overcome a filibuster.
– Harry Reid and Mitch McConnell have spent a combined 60 years in the Senate, and they've generally had an amicable relationship—but no more. Sticking points include the Democrats' attempt to oust McConnell in 2014; a super PAC led by former Reid aides is working against the minority leader in Kentucky, prompting some snarky comments from McConnell. ("Come on down. I hope you spend it all down there.”) Meanwhile, each party leader thinks his opponent is trampling Senate tradition, write Manu Raju and John Bresnahan at Politico. They say the powerful duo's relationship has degenerated into "name-calling, finger-pointing and mutual distrust." ABC's political blog the Note says the Senate is at a "boiling point." Tomorrow, Reid could turn to the "nuclear option," altering filibuster rules through a simple majority. McConnell said that would make Reid the "worst" majority leader "ever," and his team tweeted a Reid gravestone that says "Killed the Senate." Reid, meanwhile, has been frustrated by what he sees as McConnell's excessive use of the filibuster and delays of Senate affairs. It's all a big shift in an upper chamber that used to be seen as "the chummiest club in America," writes Paul Kane in the Washington Post. "The only way you get something is to become obnoxious," says Democrat Mary Landrieu. "We have turned from a Senate to a theater."