WASHINGTON — While negotiators toiled late into the night in Switzerland, scratching together a nuclear agreement with Iran, Senator Bob Corker was conducting his own tense talks back home.
The new chairman of the Foreign Relations Committee, Mr. Corker, a Tennessee Republican, was trying to marshal a bipartisan coalition for his bill to force President Obama to send any agreement with Iran to Congress for approval — a bill that could get enough votes to overcome a veto by Mr. Obama.
“I know that the diplomats in Switzerland, knowing that Congress was likely to weigh in on this deal, that was a positive thing,” Mr. Corker said in a telephone interview on Monday. “Voting for this legislation will have a positive effect on the negotiations, not a negative effect.”
There are few people on Capitol Hill more important to the White House right now than Mr. Corker, the silver-haired senator with the Southern drawl who sees himself as a bridge builder in a Senate known for polarization. At the White House, nobody likes his bill, which would give Congress a 60-day window to debate the Iran agreement before voting yes or no or taking no action, but Mr. Obama and his advisers see him as someone who might work with them to revise the legislation and ultimately make a deal.
It is no surprise, then, that the White House has spent the last few days publicly stroking Mr. Corker.
“A good and decent man,” Mr. Obama declared.
“Somebody who has considered this issue in a very principled way,” said the president’s spokesman, Josh Earnest.
The White House now views its central challenge as either negotiating a compromise with Mr. Corker or stopping enough Democrats from joining him so that he is short of a veto-proof majority, at least through June 30, the deadline to translate last week’s preliminary agreement with Iran onto paper. After that, officials said, Mr. Obama may be in a stronger position to argue the merits of the accord.
Conservatives are in the meantime watching carefully to make sure Mr. Corker does not soften. “Corker is under enormous pressure from the White House to delay or weaken his own bill,” said Dan Senor, a former Bush administration official. “But he has been strong on this issue, as has his committee and his caucus. I don’t think he’ll cave.”
While the president said in an interview over the weekend that he was open to finding a way for Congress to “express itself” as long as it did not block his ability to carry out the agreement, aides worked on Monday to discourage the impression that the president could accept even a nonbinding vote by Congress.
“The president was, in an aspirational way, suggesting that we’re going to engage with Congress, particularly those members of Congress that have done so on a principled basis,” Mr. Earnest said. “On our two principles here, about protecting the presidential prerogative and preventing the implementation of the agreement, we’re going to stand firm.”
That was fine with Mr. Corker, who said he was not interested in a nonbinding vote anyway. “No, no, no,” he said in the interview. “Having a nonbinding vote is, in essence, not of substance.”
Since joining Congress in 2007, Mr. Corker, 62, has earned a reputation as an eager deal maker who was willing to dive into the details of financial regulation, the auto bailout, entitlement spending and government-secured housing. But in a record that has made the White House concerned about whether Mr. Corker can deliver, many of those grand compromises have ended up going nowhere at a time when the two parties have appeared more intent on point-scoring and one-upmanship.
But that has not stopped Mr. Corker from trying.
In 2013, Mr. Corker was one of two Republicans who helped draft a border security amendment critical to pushing a comprehensive immigration bill through the Senate with broad bipartisan support.
“The issues that we’ve thrown ourselves into have been some of the biggest issues our nation faces, so I guess one could say, ‘Well gosh, you shouldn’t even attempt to deal with these issues because they’re too big,’ or you could say, ‘Let’s try to affect the outcome,’ ” Mr. Corker said.
Mr. Corker often seems like a senator from another time, an era when reaching out to the other side was more the norm. He sees his mandate as criticizing the president for his failings but searching for a way to forge agreement. A former construction executive and mayor of Chattanooga, he models himself after Tennessee Republicans like Senator Lamar Alexander and Howard H. Baker Jr., who was the Senate majority leader.
Gene Sperling, the president’s former national economics adviser, said Mr. Corker was always more interested in finding agreement than in passing legislation to be vetoed. “He was someone that you could confide in, be brutally candid with and even have heated disagreements with — and that it only helped build a relationship of trust and respect with him,” Mr. Sperling said.
Senator Mark Warner, a Virginia Democrat who is on the Senate Banking Committee with Mr. Corker, said the two immediately gravitated to each other as former executives, working together on various financial reforms. “In business, you get rewarded when you get to yes, and in the Senate sometimes just saying no is considered a successful outcome,” Mr. Warner said.
Senator Chris Coons, Democrat of Delaware and a member of the Foreign Relations Committee, also pointed to Mr. Corker’s private sector and local government experience. “He is not simply trying to engage in a partisan exercise to kill the deal,” Mr. Coons said.
Mr. Coons echoes other praise of Mr. Corker from Democrats, in part for what they see as his determination to make sure Congress plays its appropriate oversight role, as well as his desire to build a bipartisan coalition. When Senator Tom Cotton, a freshman Republican from Arkansas, wrote an open letter to Iran’s leadership warning about making a deal without Congress, Mr. Corker was one of only seven Republicans who refused to sign.
“When you negotiate with him, you know he wants to get something done rather than seek partisan advantage,” said Senator Charles E. Schumer of New York, the No. 3 Democrat, who said it was not uncommon for the Tennessee senator to call him at 11 p.m. and announce, “Corker here.”
Senator Benjamin L. Cardin of Maryland, the ranking Democrat on the Foreign Relations Committee, also praised Mr. Corker. “There have been many occasions where he has very much broken from the Republican message and was very much looking for a common way to move forward,” he said.
Senator Tim Kaine, Democrat of Virginia and a member of the Foreign Relations Committee, said that on a trip to the Middle East in January, he shared concerns about an earlier version of Mr. Corker’s bill.
“He was very open to having a substantive conversation about it,” Mr. Kaine said.
Mr. Corker incorporated Mr. Kaine’s suggestions, and Mr. Kaine is a now a lead co-sponsor of the legislation.