The best moments from recent debates between Senate Majority Leader Harry Reid and Senate Minority Leader Mitch McConnell. (Thomas LeGro/The Washington Post)

When Washington is in crisis and every other option has fallen to pieces — whether on rescuing Wall Street, rewriting national security rules or agreeing on a budget — Senate Majority Leader Harry M. Reid (D-Nev.) and Minority Leader Mitch McConnell (R-Ky.) are usually the ones who put it all back together.

But if the two wily 70-somethings who are trying to resolve the current crisis make a deal once again, they will do so despite an increasingly bitter and distant relationship that some say is so fraught with animosity that it endangers their talks.

The rift traces to 2010, when Reid thought McConnell wasn’t upfront about how aggressively he would try to help defeat the Democrat in his tough reelection race in Nevada. McConnell, now dealing with a difficult campaign of his own in Kentucky, is incensed that Reid appears to be more than returning the favor. In recent years, McConnell has gone around Reid to cut deals with Vice President Biden.

On the Senate floor, their rhetoric has grown so heated that their colleagues recently held the equivalent of an intervention. Off the floor, their relationship has been marked by personal slights.

On Sunday, the two leaders remained far apart. A fleeting afternoon phone call was the only sign of negotiation, although it did prompt Reid to voice a touch of hope. “I’m optimistic about the prospect for a positive conclusion,” he said just before 5 p.m. as he closed up the Senate chamber and left the Capitol.

The Senate majority and minority leaders spoke in praise of debt negotiations Monday and expressed hope that they would find a solution this week. (The Washington Post)

Still, there was no sign of progress in their standoff over federal agency budgets, which have emerged as the key hurdle in their talks, and their staff members spent the day questioning whether the other side was acting in good faith.

Some longtime friends fear that Reid and McConnell’s relationship has become so frayed that a deal might not materialize before Thursday, when the Treasury runs out of borrowing authority, setting up a potential default by the end of the month.

“There appears to be forces at work here that might cause us to get wrapped around the wheel,” said former senator Judd Gregg (R-N.H.), who retired in January 2011 after serving 18 years with both men.

Others suggest that the stakes are so high that two men with a combined 56 years of Senate experience will not allow bad blood to get in the way of a deal.

“They were hurt by one another, and they have issues that they are carrying, but I know them well enough to believe that that would take a back burner to the moment in history that they find themselves at,” said Sen. Barbara Boxer (D-Calif.), a 21-year veteran of the Senate.

The deep animosity between Reid, 73, and McConnell, 71, went public this summer, when they clashed over Democratic efforts to amend filibuster rules. McConnell called Reid “the worst leader in the Senate ever,” and Reid accused McConnell of a “breach of faith” over an earlier agreement designed to smooth the confirmation process for judicial and executive branch nominees.

Their daily clashes became so heated that rank-and-file senators requested a rare bipartisan caucus, which led to a highly unusual marathon meeting of almost all 100 senators in the Old Senate Chamber and a bipartisan pact that averted what Reid had threatened: a unilateral, party-line vote to change the filibuster rules.

Although that deal prevented what some called a “nuclear winter” in the Senate, it did little to thaw relations between Reid and McConnell.

In early September, Reid hosted a Friday night dinner for all the living Senate leaders in the Lyndon Baines Johnson Room, just off the Senate floor. The guest list, however, was restricted to those who had served as majority leader, and Reid’s guests took that as a slight to McConnell, who has been stuck as minority leader for seven years.

Although they have long been able to work together, Reid and McConnell have never been close friends. Reid often speaks in blunt terms that can be off-putting to McConnell, according to those close to both men, while McConnell is so reserved that it’s difficult to tell what he’s thinking.

But colleagues and close advisers to both senators said their relationship really started to get ugly when Reid faced an extremely difficult race in 2010. Unpopular at home and a target in the tea party wave, Reid felt that McConnell misled him about how involved he would be in trying to oust him, according to those close to the majority leader.

The National Republican Senatorial Committee, which McConnell controls as his party’s leader, even ran ads attacking Reid for living in the Ritz-Carlton when he’s in the District.

Now that McConnell is running for reelection in 2014, Reid has helped recruit a Democratic challenger, Alison Lundergan Grimes, and on Friday his friends in Las Vegas hosted a fundraiser for her, an event Reid missed only because of the stalemate over the government shutdown and the debt-ceiling deadline. A super PAC run by close advisers to Reid began running ads skewering McConnell more than 15 months before the general election.

This has infuriated McConnell, his allies say, because in 2010 he never campaigned with Reid’s opponent, tea party favorite Sharron Angle.

Reid and McConnell’s relationship has been so poor in recent months that they have used intermediaries to negotiate. When the two leaders kicked off talks Saturday morning, they were not alone — Sen. Charles E. Schumer (D-N.Y.) stood with Reid, while Sen. Lamar Alexander (R-Tenn.) was with McConnell.

Despite their differences, Reid and McConnell have taken similar paths in the Senate.

Holding the title of majority leader has been the life ambition of both men since they came to Washington in their 20s, McConnell as an intern and Reid as a Capitol Police officer working his way through George Washington University Law School. McConnell won his first Senate race in 1984, Reid two years later, and each set a course of doing all the nettlesome jobs that others never wanted to do.

Both focused their legislative careers on the Appropriations Committee, where they steered hundreds of millions of dollars to their states and directed dollars to colleagues needing help for their own home-state projects. Both did stints as chairman of the Ethics Committee, a thankless job of policing fellow senators, and both served several years as whip — spending countless hours on the floor learning every in and out of parliamentary procedure.

Over the past few days, Reid has avoided mentioning the recent fights and has focused his public comments on deals that he and McConnell have made, including creating a task force that broke through decades of turf wars among committee chairmen to reorganize oversight of national security agencies, implementing the 9/11 Commission’s recommendations. Gregg credited the leaders for shepherding the 2008 Wall Street bailout to passage, first deputizing their allies to craft the deal and then slapping some popular riders onto it after the House choked on the bill.

Each man got his party’s top job by playing the role of intensely loyal lieutenant — in contrast to deputies who often scheme behind their leaders’ backs. Reid succeeded Tom Daschle in 2005 after he lost his South Dakota reelection, and McConnell succeeded Bill Frist (Tenn.), who retired in January 2007.

McConnell is widely considered the better political tactician and Reid more of a parliamentary insider, although in the past few years those roles have been reversed.

Reid has won the political wars time and again, building the most durable Senate majority in a generation as McConnell has floundered trying to get his preferred candidates through the GOP’s nomination process. By the end of 2014, Reid’s eight-year run as majority leader will rank as the third-longest in history.

Relegated to the minority, McConnell has become the deal-closer in recent fiscal battles. His allies have accused Reid of being incapable of finishing off a deal, preferring instead to deliver insults that please liberals. That’s why the GOP leader has often sought out Biden, a former senator, to finalize pacts with the White House.

McConnell alluded to this in his only public remarks Sunday, a statement issued by his aides: “It’s time for Democrat leaders to take ‘yes’ for an answer.”

Reid’s allies have accused McConnell of being too cautious in dealing with the increasingly conservative right wing of his party. One confidant said that on several occasions the majority leader thought he had a deal with McConnell over a set of nominations, only to find out that the GOP leader had problems clearing them with rank-and-file Republicans.

That’s one reason that Reid, in July, pushed another effort to rewrite the chamber’s filibuster rules, making public the leaders’ strained relations, which had been a barely hidden secret.

Despite all that, some senators look at the past six months and see a series of bipartisan legislation that has moved out of the Senate — a farm bill, an immigration overhaul, a water infrastructure package — and predict that Reid and McConnell will get it done this time, too.

“They’ve been able to make deals when it counts,” Sen. Amy Klobuchar (D-Minn.) said Saturday on her way into Reid’s office. “Through all the toxic times, the two of them have shown the capacity to work deals.”