WASHINGTON — John A. Boehner, soon to be speaker of the House, is a conservative Midwesterner who loves his cigarettes. Nancy Pelosi is a San Francisco liberal who, upon becoming speaker four years ago, banned smoking near the House chamber, where Boehner enjoyed puffing away between votes.
She introduced organic food choices to the House cafeteria. He prefers "food that I can pronounce."
She believes in active government. He believes in shrinking government.
They are a political and personal odd couple, a pair of wary prizefighters who nonetheless have maintained a cordial relationship and respect for each other's political skills.
But when Republicans take control of the House in January, Boehner and Pelosi will swap jobs as minority leader and House speaker, and their interpersonal dynamics will be tested anew.
It will be a "forced marriage of leaders who know each other very, very well, who will be forced to work together for the good of the country," said Bradley A. Blakeman, a former aide to President George W. Bush who teaches at Georgetown University.
This high-stakes showdown of legislative and political acumen could help determine the direction of the country for years.
Republicans are well aware that they have limited time to show voters they deserve the House majority. Democrats already are eying a possible return to power with President Obama's bid for reelection in 2012.
In a town where relationships matter and deals are often brokered with a handshake, the Boehner-Pelosi union is expected to be a civil, if strained, reflection of the hyperpartisan era.
"It's not like Tip O'Neill and Bob Michel, where they go play cards together," said Rep. John B. Larson (D-Conn.), the No. 4 in party leadership, referring to past House adversaries.
"He loves this place. So does she," Larson said. "I think that's where they find common ground."
During the recent campaign season, Republicans bombarded the airwaves with attacks on Pelosi as a symbol of all that was wrong with Washington.
Democrats, including Obama, targeted Ohio's Boehner as the face of a party whose ideas had been discredited and rejected by voters two years ago.
Still, when Pelosi was elected speaker in 2007, it was Boehner who handed her the gavel, recognizing the historic moment and calling it a "high privilege of handing the gavel of the House of Representatives to a woman for the first time in American history."
And when Republicans won the majority in this month's election, Pelosi called Boehner to congratulate him. She got his voice mail.
In the weeks since the election, Boehner, 61, and Pelosi, 70, held a private meeting in the speaker's office to discuss the transition. That conference of the two House veterans was described as cordial.
Yet both leaders are headed for what appears to be inevitable conflict, determined by their own styles, and prodded by their parties' rigid bases of support, to aggressively pursue their divergent agendas.
Boehner's priorities include trying to repeal the healthcare overhaul that Pelosi considers among her greatest accomplishments.
"Because Pelosi is an aggressive partisan and is doubtless eager to be speaker again, I think it's quite unlikely to see much bipartisan cooperation between her and Boehner," said Matthew Green, a political scientist at Catholic University and author of "The Speaker of the House: A Study of Leadership."
Not that Boehner is above partisanship. He once summarized his approach to the White House agenda with "Hell, no!" And he owes his GOP majority to dozens of mostly conservative new House members who are likely to make it difficult to strike deals with Democrats.
"I think Boehner's going to be pulled really far to the right by the members of his caucus, especially the 'tea party' faction," said Rep. Chris Van Hollen (D-Md.), a party leader. "It's going to be a real test."
But the leaders do talk often, aides to both say. Like their counterparts in the Senate, Democrat Harry Reid of Nevada and Republican Mitch McConnell of Kentucky, Pelosi and Boehner frequently speak on the phone or on the chamber floor.
Republicans have gone to lengths to show they can accept their rise to power humbly. They've complained of the way Pelosi treated them when they were in the minority, and they promise to operate differently.
Democrats, however, are doubtful; they say Republicans took advantage of their power the last time they held the majority.
Pelosi offered to hold regular meetings with Boehner after she became speaker in 2007, but he declined, according to sources. Boehner's office doesn't quite remember it that way, saying they do meet, though infrequently. But Boehner has not suggested regular meetings between the two in the new Congress.
Rep. George Miller (D-Martinez), one of Pelosi's closest friends in Congress, said that Boehner "lives with the legacy of Newt Gingrich, [who] thought any bipartisan cooperation was a sign of weakness."
In the end, old routines may prove tough to break, especially when the political stakes in the new Congress are so high.
"Their caucuses are so unpredictably beyond their control that they'll need to focus mostly on how to stay in the saddle of a pair of bucking broncos," said Don Kettl of the University of Maryland.