Top Obama administration officials are scrambling to prevent a veto-proof majority for bipartisan legislation that would give Congress power to scuttle the brewing U.S.-Iran nuclear agreement.
The White House is waging a stepped-up campaign to maintain its leeway and promote the preliminary agreement reached early this month, even as lawmakers weigh changes that could increase political support for the bill in Congress.
The administration's effort, which includes briefings for lawmakers by a trio of Cabinet officials and more than 100 lobbying phone calls, arrives as top Senate Republicans are signaling plans to advance the bill quickly.
Starting Tuesday, the Senate Foreign Relations Committee will debate the bill that essentially gives Congress veto power over the hoped-for deal. A full Senate vote could arrive as soon as next week, Majority Whip John Cornyn told reporters in the Capitol on Monday. He said it's "more likely than not" to occur this month.
Across the Capitol, House Majority Leader Kevin McCarthy said the House would take up the bill quickly following Senate passage, and he predicted a veto-proof majority in that chamber.
In the Senate, Foreign Relations Chairman Bob Corker has said there are 64 to 65 current backers for his bill, close to the 67 yes votes that would be needed to overcome the veto threat that White House spokesman Josh Earnest reiterated Monday.
Corker expressed hope Monday evening that a flurry of negotiating over potential changes to the bill could get him over the top.
"We are moving in a very positive direction, and we have worked through some issues that I think give me a lot of hope that that could well be the case," he told reporters in the Capitol when asked about reaching 67 votes.
In the nearer term, cosponsor Robert Menendez, the New Jersey Democrat recently indicted on corruption charges, said he had "no doubt" the bill would clear the committee.
The White House is lobbying against the bill, which it says would undermine the sensitive negotiations with Iran. But top administration officials are also promoting efforts to show that it is keeping Congress in the loop on the effort to strike a deal to block or delay Iran's ability to develop nuclear weapons.
Obama has dispatched Secretary of State John Kerry, Energy Secretary (and nuclear physicist) Ernest Moniz, who has played a key role in hammering out technical parts of the deal, and Treasury Secretary Jacob Lew for meetings with House and Senate lawmakers.
The trio, joined by intelligence officials, held a closed-door meeting in the Capitol with House lawmakers early Monday evening, to be followed by a briefing for senators Tuesday morning.
That Senate briefing will occur just hours before Corker's panel begins formally considering the bill that would give Congress formal review of the potential final agreement, which the U.S. and Iranian officials announced in draft form in early April.
Under the bill, Obama must submit a final deal for review, and would be unable to waive or suspend congressionally imposed sanctions for 60 days while Congress decides whether to vote to block the deal or let it take effect.
White House and State Department officials on Monday launched a coordinated political effort to show that they're committed to engaging with Congress.
"The president, vice president, Cabinet members, and other administration officials have made over 130 calls to members of Congress since the announcement" of a preliminary deal on April 2, a State Department official said.
Earnest similarly cited that figure during Monday's briefing, and noted that the return of Congress after a two-week break would enable even greater discussion. "We have not been able to have as many face-to-face conversations as we would like, but that is going to change today," he said.
But reactions from House GOP lawmakers exiting the briefing with Cabinet officials in the Capitol Monday evening suggest that the administration will face an uphill battle to blunt political criticism of the talks with Iran.
"I think they would have been more persuasive to have been more factual and objective rather than in a hard-sell kind of mode," House Armed Services Committee Chairman Mac Thornberry said. "That's the way it came across to me. That plus resistance to the Corker bill increases suspicion in Congress."
Obama also met with Jewish community leaders on Monday to promote the Iran agreement.
Potential changes to the Iran Nuclear Agreement Review Act at the pending Senate markup will help determine whether wavering lawmakers such as Mark Warner and Christopher Coons back the measure.
"Should Democrats secure amendments that weaken the bill (this would probably require several Republicans), legislation that President Obama would sign might amount to little more than an orchestrated capitulation," the consulting firm ClearView Energy Partners said in a research note Monday afternoon. "Congress could have its 'vote'—a face-saving move for Hill hawks—but the vote might not stop the White House from consummating a final bargain with Iran."
In contrast, ClearView predicts that if the bill moves through the committee largely unchanged, even the support of some Democrats for the measure might not prevent the broader caucus from keeping the bill shy of the 67 votes needed to trump a veto.
Democrats including Coons and Sen. Jeanne Shaheen are seeking various changes, including removal of language that requires the president to certify that Iran has not supported or carried out acts of terror against the U.S. or U.S. citizens anywhere in the world.
That language has emerged as a key fault line. "I would have difficulty supporting the bill with the terrorism provision still in it," Coons told reporters in the Capitol on Monday.
"It is not that we are suddenly unconcerned with Iran's acts of terrorism. It is not that I don't believe Iran to be a major state of terrorism. It's that it isn't centrally at issue in this negotiation and shouldn't be centrally at issue in this legislation," he said.
Earnest also singled that provision out for criticism on Monday. "[W]e do not anticipate in the context of this agreement being able to resolve all of our concerns about Iran's terror activities. In fact, that's the reason that we're pursuing this agreement—to ensure that Iran can't obtain a nuclear weapon and then share either that nuclear weapon or some of the technology or those materials with a terrorist organization," he said.
Still, Coons said he has other issues with the bill. For instance, he wants to shorten the 60-day review period down to 30 days.
"There is a number of concerns I have about the bill as currently written that I hope will be addressed in the markup tomorrow," Coons said. "If addressed in a balanced way in the markup, I will support the bill. If the bill is dragged significantly in the other direction through a variety of amendments that have been introduced and could be adopted, then I will not vote for it."
This story has been updated.
Sarah Mimms and Rachel Roubein contributed to this article