Sen. Bob Corker, Senate Foreign Relations chairman, arrives for a briefing on Iran nuclear negotiations with Secretary of State John Kerry and President Obama's chief of staff Jack Lew in the Capitol on April 14, 2015.
Bill Clark—CQ-Roll Call/Getty Images
By Alex Rogers
Updated: April 14, 2015 2:21 PM ET

Over the next 10 weeks or so, Tennessee Sen. Bob Corker can’t afford a mulligan. Lucky for him, according to occasional golfing buddy and Georgia Sen. Johnny Isakson, he “doesn’t need ‘em.”

In that time, Corker will be “one of the most important people in the world,” as my colleague Massimo Calabresi writes in a magazine profile this week, as he attempts to ensure congressional oversight into a global debate on Iran’s nuclear program the Obama Administration would rather wage on its own.

As chairman of the Senate Foreign Relations Committee, Corker has the delicate task of crafting a 67-vote supermajority to beat back a veto threat on his bill, which the Administration has worried could imperil the chances of reaching a final deal by a June deadline. Corker struck a major agreement Tuesday, when the committee will take up his bill and introduce a series of amendments that could endanger consensus. But senators on both sides of the aisle are confident that Corker is well suited to the challenges ahead.

“There’s not a better horse to bet on in the United States Senate than Bob Corker,” says Isakson, a Republican member of the committee.

At first glance, Corker is an unlikely player in international affairs. A successful construction company owner, former Chattanooga mayor and head of Tennessee’s finances, Corker had no foreign policy experience before coming to the Senate in 2007. While a student at the University of Tennessee, Corker wasn’t even interested in politics, according to his roommate, Jimmy Haslam, who used to call Corker “Thor” because he “looked like a little Viking.” But his interests eventually evolved and after an introduction from Haslam, Corker met with Tennessee Sen. Lamar Alexander in 1993. The pair talked for an hour and a half as they walked down the beach at Hilton Head, South Carolina, discussing whether Corker should run for Senate or governor.

“He’s never been afraid of big jumps,” says Alexander, who thinks the two-term senator would be “terrific” as Secretary of either the State or Treasury departments. “In a way he’s perfectly named—Corker.”

Corker popped to the ranking Republican position on the committee in 2013 and became chairman when Republicans took the Senate this year. To overcome his initial lack of expertise, Corker has engaged in policy discussions with numerous foreign policy experts, including former Secretary of State Henry Kissinger, who has breakfast with him every two or three months. Corker also travels extensively; he told TIME in February that he had traveled to over 63 countries. Haslam, now the owner of the Cleveland Browns, says his longtime friend flies commercial on his trips to the Middle East with usually one staff member. “Bob’s not a hot dog,” says Haslam. “He gets the job done.”

Corker’s temperament may serve him well as debate over U.S. foreign policy no longer ends at the water’s edge. Democrats are still smarting from Arkansas Sen. Tom Cotton’s direct letter to Iranian leaders and House Speaker John Boehner’s invitation of Prime Minister Benjamin Netanyahu to speak to Congress. One of seven Republicans who didn’t sign Cotton’s letter, Corker has garnered praise from Democrats. Maryland Sen. Ben Cardin, the top Democrat on Corker’s committee, calls Corker a “serious legislator” and an “ideal fit” for the panel’s chairmanship.

“I think that he is trying to use that position in the best tradition of the U.S. Senate to bring as much unity on behalf of foreign policy as possible,” Cardin told TIME last week. “And recognizing that’s challenging today, I think he’s done a really good job on his bill on the congressional oversight of the nuclear agreement. It’s one in which I hope we can find common ground. I think we’re very close to that.”

Introduced with Democratic Sens. Bob Menendez and Tim Kaine and Republican Sen. Lindsey Graham as cosponsors, Corker’s bipartisan bill threads the needle by establishing an order of review, preventing the president from waiving Congress’ economic sanctions against Iran for 30 days, according to a Corker aide, and up to 52 days if Congress passes a bill and the president vetoes it. If the deal is submitted late, after July 9, the review period reverts to 60 days, according to the aide. If President Obama accepts it, the Administration would be required to tell Congress every 90 days if Iran is still keeping up its end.

“We have reached a bipartisan agreement that keeps the congressional review process absolutely intact and full of integrity,” said Corker on MSNBC’s Morning Joe Tuesday. “On behalf of the American people we want to make sure that if a final deal is reached it lays before Congress, so we have the opportunity to go through every detail.”

Corker has worked for months to bring Democrats on board. The bill originally had called for a vote to approve or disapprove of the deal—now there is the option to not act, Menendez told TIME. Another priority—pushed by New York Sen. Chuck Schumer, according to the New York Times—was ensuring a 60-vote rather than a 51-vote threshold for any resolution of disapproval or agreement, ensuring that Congress spoke in a bipartisan manner. Kaine claims credit for limiting the bill to only sanctions imposed by Congress, rather than the Administration or international bodies. Still, just last week Cardin said he had three major areas of concern: “the time for review, the limitation of presidential powers during the review, and to the statute issues that are not directly related to the nuclear agreement.”

So over the past few days and up through Monday night, Corker has worked to close the gaps with Democrats, reportedly softening requirements that Iran isn’t directly sponsoring terrorism against the United States and loosening restrictions on the original timetable for a 60 day congressional review period.

The negotiations have appeared to assuage Democratic concerns. On Tuesday, White House Press Secretary Josh Earnest said that Obama’s veto threat would be revoked—a stunning turnaround—if some of the changes the White House has proposed, including the timetable and terrorism language, make it through committee.

“We have to see what comes through the committee process,” said Earnest. “What we have made clear to Democrats and Republicans is that the President would be willing to sign the proposed compromise that is making its way through the committee today.”

Corker’s immediate challenge now is to navigate a series of controversial amendments from Democrats and Republicans alike. One from Connecticut Democratic Sen. Chris Murphy would allow President Obama to waive sanctions during the 60 days if a “failure to do so would be a breach of the final comprehensive agreement,” according to Murphy spokesman Chris Harris. Another by Isakson would make a condition of sanctions relief “fair and appropriate compensation” to Americans who were terrorized in the 1979 Iranian hostage crisis. And Florida Republican Sen. Marco Rubio will introduce an amendment making approval of the deal dependent on Iran’s recognition of Israel’s right to exist, according to the New York Times.

Some of those amendments are nonstarters with the Administration, which has launched a full-scale lobbying effort on Capitol Hill. Secretary of State John Kerry, Treasury Secretary Jacob Lew and Moniz briefed House members in a classified session Monday and are expected to hold another for senators on Tuesday, according to the Times. They are trying to convince lawmakers to agree to a framework agreement that couldn’t be subject to a wider divergence of opinion. Critics like Cotton, a foreign policy hawk and Iraq combat veteran, believe the deal could eventually lead to a nuclear confrontation. The Administration argues it could lead to a safer world, lengthening the time it would take for Iran to produce such a bomb over the next decade from three months to a year, giving America’s allies more time to forcefully respond.

Corker’s knack for jumping into the hairiest policy debates hasn’t always been a success, including in his early efforts to negotiate the auto company bailout and Dodd-Frank financial regulation reform. “He’s a guy who views things without the partisan lens and from a very practical approach,” says Josh Holmes, Senate Majority Leader Mitch McConnell’s former chief of staff. “I think in some ways early on it made him a target for Democrats to try to wedge the best deal out of.”

“I will say that Corker is amongst the most intelligent senators on the Hill,” adds Holmes. “He learns a great deal from each one of these interactions.”

Corker did seal a deal during the 2013 immigration reform debate, helping craft border security legislation that the Senate incorporated and passed before it died in the House. Menendez told TIME he “swallowed” Corker’s “odorous” amendment because he agreed with his colleague that it would “guarantee us a big vote and that the greater good was better served by accepting what he could bring along with him.”

Corker’s goal is essentially the same now: to convince a wide swath of Congress to get to “yes” despite their reservations. Menendez, who has “tag teamed” members on the bill on the Senate floor, says Corker is a dogged negotiator.

“He’s tenacious going to anyone on either side of the aisle making his case,” says Menendez. “And he won’t stop. If you say no to him, he’ll ask you why and then try to argue away the concern. If you say I’m thinking about he’ll probably come back to you another 10 times.”

With reporting by Maya Rhodan and Massimo Calabresi/Washington, D.C.

Contact us at editors@time.com.

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