The Republican Congress is demanding to be heard on a nuclear deal with Iran despite President Barack Obama’s warnings. But it’s the president’s Democratic allies in the Senate that hold the keys to any Iran bill.

Republicans have written legislation they think can move quickly through the Senate. It would give Congress a critical role in accepting or rejecting a deal with Tehran.

But they need Democrats to proceed with the bill, and the White House is sure to start twisting arms in the party to try and keep the measure off the Senate floor. Several Democrats have previously said they would support the legislation, but now that Obama can argue he’s made progress, Democrats will have to decide whether they want to openly rebuke the administration’s diplomatic efforts.

The new top Democrat on the Senate Foreign Relations Committee, Ben Cardin of Maryland, sounded like he was still making up his mind. He said he was open to moving forward, but cautioned he needs to study how legislation written by Sen. Bob Corker (R-Tenn.) interacts with the complex non-proliferation framework struck by Iran, the United States and five other global powers. Cardin noted that he hadn’t yet spoken to the president about his new role on the committee.

If he determines that Corker’s bill won’t break the fragile agreement, Cardin could end up supporting it, particularly if Corker is open to tweaking it further to satisfy Democrats.

“Congress does have a right to review the agreement, the sanctions are imposed by Congress. A review process established by Congress makes sense,” Cardin said late Thursday afternoon.

But, he added a critical disclaimer: “I want it to strengthen the president, not weaken the president, I don’t want it to undermine negotiations.”

If enough Democrats go along with Corker, it’s on to the Senate floor and then the House, where Speaker John Boehner (R-Ohio) is open to taking up the proposal, which would give lawmakers the power to approve or reject the agreement’s lifting of sanctions on Iran.

But if the bill begins working its way through Congress, Obama has warned lawmakers it could undermine a deal.

“They’ll be working hard to peel them off, but I think they’ve got a fairly hard case to make because [the deal is] so vague,” said John Thune of South Dakota, the No. 3 Republican in the Senate. “It’s going to depend a lot on how strong and resilient these Democrats are when the administration starts breaking arms.”

Indeed, Obama indicated a full-court press to lobby against the bill was already in the works. With Congress in the middle of a recess, both Corker and the White House will be gauging support for the bill, which Corker intends to take up in committee on April 14.

To win a veto-proof majority, Corker will have to reassure Cardin and fend off White House pressure on Democrats to hold off on voting for Iran legislation.

Other Democrats, like Sen. Tim Kaine (D-Va.), reemphasized their support for legislation even in the wake of the historic announcement, calling the Corker measure one that “sets up a clear and constructive process for Congress to weigh in on any final deal that touches upon the statutory sanctions Congress has enacted.”

Obama challenged lawmakers preemptively in his Thursday speech, asking whether a verifiable deal with Iran “is a worse option than another war in the Middle East.”

“If Congress kills this deal, not based on expert analysis, and without offering any reasonable alternative, then it’s the United States that will be blamed for the failure of diplomacy, international unity will collapse, and the path to conflict will widen,” Obama added.

And shortly after he spoke his top aides began working the phones. Sen. Ron Johnson (R-Wis.) got a phone call from U.S. Ambassador to the United Nations Samantha Power urging him to keep an open mind, Sen. Chris Murphy (D-Conn.) got a telephone briefing from Deputy Secretary of State Tony Blinken and Obama himself called Senate Democratic Leader Harry Reid (D-Nev.) and said he’d soon be in contact with other congressional leaders, including Boehner and Senate Majority Leader Mitch McConnell (R-Ky.).

Many Republicans won’t be swayed. Johnson said he was trying to keep an open mind but also suggested that Corker’s bill doesn’t go far enough, suggesting instead that Congress should declare the nuclear deal a treaty that must be ratified by the Senate.

“We could have a very simple bill that basically says, that no matter what President Obama says, we are going to call this a treaty and we are going to ratify this as a treaty,” Johnson said, adding that he’s “concerned” about the complexity of Corker’s bill.

Many of Johnson’s colleagues went straight into the blistering criticisms, summoning their choicest rhetoric to pan Obama’s negotiating acumen after railing against the ongoing negotiations for months. Sen. Tom Cotton (R-Ark.) said no agreement was struck, describing Thursday’s announcement as simply a “list of dangerous concessions.”

And in a telephone interview, Sen. Mark Kirk (R-Ill.) reiterated that his leaders should give his sanctions bill a vote and blasted the president’s announcement and a top State Department negotiator, Wendy Sherman.

“I would say that Neville Chamberlain got a lot more out of Hitler than Wendy Sherman got out of Iran,” Kirk said.

Meanwhile, Republican presidential contenders said the administration was pursuing a seriously flawed nuclear deal that gives away too much while getting little in return. “These negotiations began, by President Obama’s own admission, as an effort to deny Iran nuclear capabilities, but instead will only legitimize those activities,” former Florida Gov. Jeb Bush said in a statement. “I cannot stand behind such a flawed agreement.”

Wisconsin Gov. Scott Walker, was more critical, saying the agreement “rewards an enemy, undermines our allies and threatens our safety.” And Sen. Marco Rubio called it “just the latest example of this administration’s farcical approach to Iran.”

The main event, though, will be courting Democrats. And some aren’t inclined to support Corker. Murphy said that as long as the president’s negotiators are telling him that Iran votes would scuttle negotiations, he will hold off on supporting congressional approval legislation.

“Corker’s desire to move his bill exists independent of the contents of the deal. Bob just believes he’s got to pass this bill. I disagree,” Murphy said. “My feelings about the Corker proposal are completely interdependent on the level of concern from our negotiators.”

Indeed, with the framework in hand and some members like Murphy already satisfied with giving the administration room and time to negotiate, Obama’s outreach will focus on Democrats who have signaled support for either Corker’s bill or one that would snap sanctions back on Iran if it reneges on any part of an agreement.

But on-the-fence Democrats are also waiting for a signal from leaders in Tehran. Will Iran step forward and publicly embrace Obama’s description of an agreement that would pull apart two-thirds of the country’s centrifuges? And will Iran accept the president’s claim that the deal prevents Tehran from making a nuclear weapon?

That, said Rep. Brad Sherman (D-Calif.), is the sticking point.

“If the Iranians do not publicly agree to what the president says they’ve agreed to, then I’m ready to vote for both bills,” Sherman said in an interview. “If Iran cares what Congress does, the first step is to publicly agree to what the president puts out.”

The White House has repeatedly lobbied Democrats away from supporting either bill on the Senate floor, and as McConnell prepares his chamber to vote on Corker’s bill, Obama and his aides are moving quickly to stifle Democratic support. The White House is less worried about members like Murphy and Reid, and instead will concentrate on members like Cardin and Democratic-leader-in-waiting Sen. Chuck Schumer of New York, who’s a co-sponsor of Corker’s bill and Kirk’s sanctions legislation.

Schumer didn’t tip his hand on Thursday.

“Secretary Kerry and Secretary [Ernest] Moniz have worked long and hard and their announcement deserves careful, rigorous and deliberate analysis. I’ll be giving the framework a very careful look,” Schumer said.

By Politico