Senate Minority Whip Richard Durbin “really showed his skills as a leader within our caucus,” one of his fellow Democrats said. (Pablo Martinez Monsivais/AP)

President Obama’s legislative victory this week on the Iran nuclear deal may not have occurred without a phone call in mid-July from Sen. Richard J. Durbin (D-Ill.), shortly after international negotiators in Vienna had signed the historic agreement.

Details of the pact had barely begun coursing through Washington, and few Democratic lawmakers had yet taken an explicit position ahead of what promised to be an intense congressional debate — including Durbin, the Senate minority whip.

But with that call, he quietly started the most consequential effort in his decade-long tenure as the Senate Democrats’ chief vote counter. “I want to do this,” he recalled telling White House Chief of Staff Denis McDonough. “Let me start finding out where members are and let you know.”

That effort began with Republicans and conservative advocacy groups promising a full-court press against the deal, while many Democrats were openly skeptical. It ended Thursday in the Senate, with Democrats building a firewall with 42 of 46 caucus members holding together to block a Republican disapproval measure, sparing the president from having to unsheathe his veto pen.

Where lawmakers stand on the Iran deal

For that, Obama can thank an all-hands-on-deck approach from his own deputies, but also from his fellow Illinoisan, who became one of the first senators to endorse the deal and then deployed a soft touch to monitor, inform and gently cajole colleagues into backing the controversial centerpiece of the president’s foreign policy agenda.

“He facilitated members going through their own process and didn’t big-foot anybody,” Sen. Brian Schatz (D-Hawaii), an early deal supporter, said of Durbin. “He could have overdone it, or he could have underdone it. He really showed his skills as a leader within our caucus.”

The unusually divisive nature of the issue — particularly the staunch opposition from pro-
Israel groups — made the decision a delicate one for many Senate Democrats; party leaders were no exception. While Minority Leader Harry M. Reid (Nev.) privately told the White House in late July that he would be supportive, it was three more weeks before he announced that support publicly. Patty Murray (Wash.), the Democratic conference vice chairwoman, waited even longer, and Charles E. Schumer (N.Y.), the conference chairman and Reid’s heir apparent, came out against the deal in early August.

In his Capitol office Thursday evening, shortly after the filibuster vote that short-circuited the opposition, Durbin studied a dog-eared 8-by-2-inch card listing the 46 members of the Democratic caucus. He had filled it out before leaving Washington for the four-week August recess and had kept it on his person since.

“The way this has been done 99 times out of 100 is, I go down the steps, sit down in Harry’s office, and we pull out one of these cards and go through it and say, ‘Who you gonna call? Who you gonna call?’ ” Durbin said. “But this was different: I was initiating it.” 

Based on his own read of the caucus, Durbin initially listed 25 Democratic senators in favor of the deal, and two against: Schumer and Robert Menendez (N.J.). Everyone else was up in the air, and there were reasons for pessimism: Reid wasn’t a sure bet; Schumer was a wild card; and Benjamin L. Cardin (Md.), influential because of his top post on the Foreign Relations Committee, had told Durbin, “Put me down as leaning no, and keep me there.”

Meanwhile, Republicans were nearly unanimous in opposition, anti-deal groups including the American Israel Public Affairs Committee were pledging to spend tens of millions of dollars on ads opposing the deal, and Durbin’s clout within the Senate had been in question for months, since Schumer emerged from Reid’s March retirement announcement as his presumptive successor.

Here's what's in the Iran nuclear deal, and what happens next. (Gillian Brockell and Julio C. Negron/The Washington Post)

In the weeks after the deal was finalized, Durbin assembled an informal whip team of pro-deal Democrats — an unusual move in the Senate, where keeping track of a few dozen members is typically a straightforward matter. On this vote, little was taken for granted.

Shortly after the deal was announced, Durbin arranged private briefings for Democrats, separate from the all-senators briefings being delivered by Cabinet officials. One featured key U.S. negotiators, where specific questions about the talks could be answered. More crucial, several senators said, was a briefing arranged with top diplomats from the international coalition involved in the deal, alongside U.S. diplomats.

“If members really believed there was a better deal waiting in the wings, they would have voted no,” said Sen. Chris Murphy (D-Conn.), a whip team member. “That meeting was as close to a turning point as there was in the Senate, because the ambassadors were clear as day in their assessment that there would be no second negotiation.”

As the Senate readied to leave Washington for its August recess, there were encouraging signs: Kirsten Gillibrand (D-N.Y.) announced her support of the deal, bucking speculation that she might bow to influence from Schumer and concerned Jewish constituents. And when Schumer announced his opposition later that day — earlier than deal supporters had hoped — no other senators immediately joined him.

But there were deep worries about what the recess might bring. Durbin was determined not to repeat the mistakes of 2009, when lawmakers were blindsided by angry constituents ahead of votes on health-care reform.

“The feeling was that during 2009, everyone went their separate ways and just crossed their fingers,” Murphy said. “The decision was made that the whip operation and the White House were going to keep tabs on undecided members throughout that break.”

An Obama administration team, headed by deputy national security adviser Ben Rhodes and run out of an “anti-war room” in the basement of the West Wing, stood ready to meet any request from any lawmaker. Obama himself spoke with 70 members of Congress during August, including dozens he called while on vacation in Martha’s Vineyard.

Early on, the strategy to defend the deal focused on the House, where Minority Leader Nancy Pelosi (D-Calif.) was confident that she could hold together the roughly 150 Democrats necessary to preserve a presidential veto. But as the White House worked to assuage senators, that chamber emerged as a bulwark.

The gestures were sometimes subtle. Energy Secretary Ernest Moniz flew to Detroit in early August to meet with Michigan’s two senators and leaders of its Jewish community and explain the technical underpinnings of the deal. Moniz also called a North Dakota radio show hosted by the brother of Sen. Heidi
Heitkamp (D-N.D.) and gave an interview to the Missoulian newspaper shortly after the Israeli consul general to the region visited the home state of Jon Tester (D-Mont.) to lambaste the deal.

Durbin, Murphy and a senior Obama administration official each said there was no effort to manage the timing of senators’ announcements in favor of the deal, though they came at a steady clip through the August recess up until senators returned Tuesday to Washington, thus blunting any momentum opponents might have mustered.

“One of the things that Dick said to each member was, make your own decision and announce your own decision in your own way on your own time frame,” Schatz said. “People were prepared to bristle at being corralled, and it didn’t happen.”

But that didn’t mean no one was paying attention. As August drew to a close and it remained unclear whether Obama would need to veto a disapproval resolution or whether the Senate would be able to bottle it up, Reid — now fully engaged — began strategizing to hold 41 senators together for a filibuster. Durbin, meanwhile, started sending daily texts to undecided colleagues.

“I’d say, ‘Here’s where we are: We’re at 34. You should know that the latest poll is this, and you should know that Dick Cheney’s announced that he’s going to come out against it,’ ” he said. “Three or four sentences, just to kind of keep in touch.”

He also probed back channels for intelligence. Murphy, for instance, spent the last week of recess on a Middle East fact-finding trip with Gary Peters (D-Mich.), a freshman who was among the last senators to make a decision. “I’m texting [Murphy], saying, ‘How we doing? Give me a signal!’ ” Durbin said. But Peters remained studiously undecided.

Meanwhile, the White House had sent two officials, National Security Council negotiator Paul Irwin and Jewish community liaison Matt Nosanchuk, to Ann Arbor to do a public Q&A at the University of Michigan just ahead of the Labor Day weekend.

On Tuesday morning, with a filibuster hanging in the balance, Peters released a 2,200-word statement backing the deal.