Washington being Washington, the hottest relationship in town does not revolve around sex or even the next presidential election; it is the political courtship of old antagonists, Barack Obama and John McCain.
Political relationships, especially those involving the president, are the sustenance of the American capital. Sometimes they are poisonous: President Lyndon B. Johnson and Robert F. Kennedy, as captured in the latest volume of Robert A. Caro's biography of L.B.J. At other times, they are lopsided, as when President Bill Clinton dominated Newt Gingrich under the guise of working together. And every now and then, there are adversarial yet symbiotic relationships that, on balance, get things done: President Ronald Reagan and Tip O'Neill in the 1980s, for example.
The association between Mr. Obama and Mr. McCain is different. But it may be Washington's most important in many years.
Mr. McCain, 76, whose political resiliency is rivaled only by such luminaries as Bill Clinton and Richard Nixon, is the most pivotal figure in the Senate today. He often is more central than the Senate party leaders, Mitch McConnell, a Kentucky Republican, and Harry Reid, a Nevada Democrat, or the self-styled new power broker, Charles E. Schumer, Democrat of New York.
When Mr. McCain is with the president -- on immigration and in brokering the recent deal to secure Senate approval of stalled Obama nominees -- they can usually trump the political right. When he is against him -- sabotaging Mr. Obama's plan last year to nominate Susan E. Rice as secretary of state -- the White House rarely prevails.
Their previous strains predated 2008, when they vied for the presidency. Mr. Obama saw his Republican rival as an embittered, compromised maverick who treated him as an undeserving upstart. After he lost that election, Mr. McCain saw Mr. Obama as naïve, aloof and surrounded by too many sycophants.
In 2011, there was a move to détente after Representative Gabrielle Giffords of Arizona was shot. That, however, was "a false start," Mr. McCain recalled in an interview last week.
This time, political convenience broke the ice. A re-elected president soon realized that without the support of a small core of Senate Republicans, any agenda was doomed. Mr. McCain, who moved right to fend off a Tea Party primary challenge in 2010, was itching to reclaim his maverick persona and wage a two-pronged battle: against the isolationists and the political right of his own party and against the national-security left wing in the Democratic camp.
Since the January inauguration, Mr. Obama and Mr. McCain have met a dozen times. In half of those occasions, they were either alone or with only a few other principals. Although the discussions were usually about immigration policy, they invariably ranged more broadly.
There are huge tests ahead, especially the battles this autumn over the federal budget and raising the debt ceiling. Mr. McCain, the defense hawk, despises the across-the-board cuts to defense and discretionary domestic spending required under the set of cuts known as sequestration and wants to help forge a compromise replacement involving more taxes and cuts in entitlements.
The odds are against that happening; most House Republicans are more eager for an economy-threatening standoff than for an accord. The only slim hope is a deal, led by the White House and a small group of McCainites.
Mr. McCain also wants to help Mr. Obama fulfill his promise to close the detainee camp for terrorism suspects at Guantánamo Bay, Cuba. He says political conditions are much different than they were four years ago when there was a similar effort.
"The difference between 2009 and 2013 is the administration now has a plan," he says.
Last month, the five-term senator traveled to Guantánamo with the Senate intelligence committee chairwoman, Dianne Feinstein, and the White House chief of staff, Denis McDonough.
Mr. McDonough, whom Mr. McCain knew as a midlevel aide to Tom Daschle when Mr. Daschle was the Democratic Senate leader, is a glue that binds the Republican and the administration. He and Mr. McCain talk as often as five times a day. In addition, the Republican senator has a great fondness for Vice President Joseph R. Biden Jr. and a good working relationship with Secretary of State John Kerry and is a fan of Samantha Power, the U.N. ambassador-designate.
He is also an unrelenting critic of most of Mr. Obama's foreign policy. He sees the president as indecisive or soft on Syria, Egypt and Afghanistan. He has a long-running feud with Gen. Martin E. Dempsey, the chairman of the Joint Chiefs of Staff.
He has no regrets about torching Ms. Rice's appointment as secretary of state and continues to suggest that she dissembled on the terrorist attack last year against a U.S. mission in Benghazi, Libya. When she was tapped to head Mr. Obama's National Security Council, Mr. McCain wrote a Twitter post saying that he would make "every effort" to work with her. She contacted him, they had a cordial meeting, and he asked her to discuss Syria with one of his confidants, the retired general Jack Keane. Ms. Rice met with General Keane: "I can't ask for anything more," Mr. McCain says.
He is as eager to take on the isolationists led by Senator Rand Paul within his party. In an April speech at the Center for a New American Security, he focused criticism on his fellow Republicans. He has disdain for much of the movement right and little regard for Mr. McConnell.
In the interview in his Capitol hideaway office last week, the never combat-shy Mr. McCain seemed to revel in his reclaimed persona and his multifront battles. He suggests, however, that his style is changing.
"The biggest mistake I used to make was getting personal," he says, declaring that his role model now is Ted Kennedy, the late Democratic senator, who was a friend.
One prominent Democrat, who knows both Mr. Obama and Mr. McCain well, is certain the senator genuinely wishes to work with the president. Noting that for all the assistance of Mr. McDonough or even Mr. Biden, at this level, interactions ultimately depend on principal-to-principal connections, and the politician, who declined to be identified, worries that Mr. Obama does not do relationships well.
Asked about that, Mr. McCain paused, then acknowledged that the president is not a "schmoozer" like his predecessors Mr. Clinton or Mr. Reagan.
"He's willing to compromise but sometimes not sure he knows exactly how to do it," Mr. McCain says. "We can help."
This article originally appeared in The New York Times.