Secretary of State John Kerry spent a second day Tuesday urging US lawmakers not to interfere in sensitive Iran nuclear talks, hours before senators vote on giving Congress a say on the accord's fate.
As the Obama administration faced skepticism in closed-door meetings with House and Senate members, a compromise emerged on a Senate measure that would shorten the period that Congress would have to review the final deal.
Senate Foreign Relations Committee chairman Bob Corker said the total review period would be reduced to 52 days, from the 60 days in earlier drafts of the bill.
The period includes a 30-day review, plus 12 days for a possible veto by President Barack Obama and a 10-day window for an attempt to override such a veto.
"My sense is we're moving towards a strong support in committee," Corker told reporters before senators met behind closed doors with Kerry.
The idea is that the compromise legislation would bring more Democrats on board, potentially building a veto-proof majority.
Senate Democrat Chris Coons said he was encouraged by the shift from a 60-day review to 30 days, "so that there's less of a risk that it will drag on."
But he warned that including poison-pill amendments in the legislation -- such as one being considered that would require Iran to recognize the state of Israel -- would lose his support.
"What this bill provides is a congressionally enacted, focused and concise framework for the exchange of information and the review by Congress where at the end of the day, if a veto by the president of a resolution of disapproval is not overridden, the agreement proceeds," Coons said.
The framework, reached in Lausanne, Switzerland, marked a major breakthrough in a 12-year standoff between Iran and the West, which disputes Tehran's denial that it is seeking to acquire nuclear bomb.
Global powers must resolve a series of difficult technical issues by a June 30 deadline for a final deal, including the steps for lifting global sanctions imposed on Iran, and remaining questions over the possible military dimensions of its nuclear program.
While some Democrats pressed Kerry on why lawmakers should let the White House move ahead with the Iran accord without their involvement, the top US diplomat provided a reasoned, comprehensive argument for doing so, House Democrat Jan Schawosky said.
Kerry made "an irrefutably compelling case on why we need to do this, and very clear how detailed this agreement is," Schakowsky told reporters after emerging from the briefing.
"I think that there is no doubt that the House of Representatives can sustain a veto if something comes from the Senate that would undermine this agreement."
But some critics remained hostile to the administration's urging that lawmakers step back.
"They want Congress just to go away," said Senator Mark Kirk, a hawkish Republican on the Iran issue and author of a bill that ratchets up sanctions on the Islamic republic.
But House Democrat Sheila Jackson-Lee emerged from the Kerry briefing saying "it was not oppressive" or domineering.
"This (deal) is a seismic change against nuclear proliferation, and I challenge the critics to tell me why it is not."