But with members leaving town until September, the administration is losing its greatest asset in the lobbying campaign: proximity.
“The recess is not good for the administration,” Rep. Brad Sherman, D-California, said recently after an administration briefing.
The campaign has yielded some crucial endorsements, with supporters confident the president has enough votes to sustain a veto of a resolution of disapproval.
But now, members will now hear from constituents and outside groups arrayed on both sides of the deal.
“[The administration has] the most incredible home field advantage ever for the first two innings,” Sherman said. “For the other seven innings it’s on a neutral field.”
“There will certainly be an intensive lobbying campaign by both sides during August recess,” said Rep. Adam Schiff, the ranking Democrat on the House Intelligence Committee, who has not yet announced his position.
Citizens for a Nuclear Free Iran, a pro-Israel group financially supported by AIPAC, has a multi-million dollar national ad campaign underway in 35 states.
“The more that people look at this deal, the less they support it,” said spokesman Patrick Dorton. “We hope that the American public and members of Congress will look at all the fine print and details.”
“I’m going to try to ignore the politics, and I’m going to try and ignore my own emotions,” he said Thursday after meeting with Obama. “I’m going to do what I think is the right thing.”
Speaking to grassroots supporters of the Iran deal Thursday, the president acknowledged that the recess would be a tougher climate to woo members.
“They start getting squishy when they feel the political heat,” he said.
While endorsements continue to trickle in — Rep. Dan Kildee, D-Michigan, who represents the family of Amir Hekmati, an American imprisoned in Iran, announced his support Thursday — some members have also come out against the deal.
Others are planning to wait until September before making a decision.
“I’m going to take advantage of that adequate review period before announcing where I am,” said Rep. Steve Israel, D-New York, who said he’s “skeptical” of the deal.
He’ll have a few more weeks before the White House starts calling.
ABC's Ali Weinberg and Arlette Saenz contributed to this report.