Members of Congress who have squared off on the Iran nuclear deal since its inception strategized Wednesday in preparation for President Trump's highly anticipated announcement on its fate.

Leading House Republicans huddled with national security adviser H.R. McMaster Wednesday evening for a classified briefing on the administration's plan for the 2015 agreement. Emerging from the meeting, McMaster told reporters simply that it had been "Great, thanks."

If Trump decides to decertify Iran's compliance, as expected, Congress will have 60 days to decide whether to "snap back" sanctions that were lifted in exchange for curbs on Iran's nuclear program. If sanctions were reimposed, despite the International Atomic Energy Agency verifying eight times that Iran has lived up to its end of the deal, the United States would be in breach of its commitments. In effect, it would be walking away unilaterally.

House Democrats met earlier in the day with former secretary of state John F. Kerry and former energy secretary Ernest Moniz, who were the primary negotiators of the deal made between Iran and six world powers. Wendy Sherman, another key negotiator, was also present. Jacob J. Lew, the former Treasury secretary, joined the discussion by phone.

Joining them were ambassadors to the United States from France, Germany and Britain — three European nations that also were parties to the multilateral agreement and have urged the United States not to abandon the deal so arduously negotiated.

Democrats are fiercely opposed to Trump's determination that Iran is not meeting its commitments and insist the agreement must remain intact to survive. Many will not even discuss what congressional debate might follow if Trump decertifies, instead focusing the arguments for certification.

But several key Democrats suggested there might be room to negotiate with Republicans about beefing up the deal without eviscerating it.

The involvement of Congress is not required under the agreement known as the Joint Comprehensive Plan of Action, which was approved by the United Nations. But it is a requirement of U.S. law.

Rep. Elliot Engel (N.Y.), the top Democrat on the House Foreign Affairs Committee, said he would consider modifying the Iran Nuclear Agreement Review Act so the president certifies Iran's compliance less frequently than every 90 days now, or using different standards. He would not say whether he would be open to other changes, stressing new conditions might violate the deal.

France, Germany and Britain, despite their opposition to Washington backing away from the deal, have told U.S. lawmakers that they could join discussions on constraining Iran's long-term nuclear ambitions, according to one congressional Democratic aide.

Republicans have complained that the deal delays Iran's nuclear ambitions but could allow Iran to resume its nuclear program after certain restrictions expire. Iran has denied it wants to build a nuclear bomb, and the agreement commits it to never build one, but various "sunset clauses" would allow Iran to amass greater stockpiles of fissile material that raise concerns.

Trump, Secretary of State Rex Tillerson and Senate Foreign Relations Committee Chairman Bob Corker (R-Tenn.) have been working for months hashing out a package to present to Congress, only recently bringing in Senate Majority Leader Mitch McConnell. Sen. Benjamin L. Cardin (Md.), the ranking Democrat on the Senate Foreign Relations Committee, learned of their work a little over a week ago.

Cardin went to the State Department on Wednesday to meet with Tillerson. Cardin's spokesman said the purpose of the meeting was to go over the administration's plan for the nuclear deal. Tillerson's spokesman said they discussed several issues, including Iran. Tillerson is expected to reach out to other members of Congress in coming days to brief them on the administration's intentions on the nuclear deal.

Some Democrats complain it would be difficult to join in a bipartisan plan to restrain Iran's nuclear ambitions. Trump's strenuous opposition to the agreement forged by the Obama administration — which Trump criticized during the campaign as the worst deal ever — means any attempt to change the conditions would be interpreted by Tehran as an effort to blow it up.

"The effect of what the president has done has really been to constrain our freedom of action," said Rep. Adam B. Schiff (Calif.), the ranking Democrat of the House Intelligence Committee, "because steps we might have taken to constrain Iran's malevolent activity will now be viewed through the prism of the president's hostility to the nuclear deal. Ironically he may have limited our ability to confront Iran, rather than expand it."

In addition, Trump could at any time decide not to waive the nuclear-related sanctions again — a decision he must make every 120 days under U.S. law. Many Democrats believe that is more likely to happen if Congress does not act to make changes to the existing agreement.

"That's what we have to consider," said Rep. C.A. Dutch Ruppelsburger (D-Md.), the former top-ranking Democrat on the House Intelligence Committee. "But the good news is if we can get to the American public like we did on health care . . . and we have our military, Cabinet members who already think the deal is working, we hope he would re-evaluate."

In this environment, many Democrats believe working on the periphery of the deal could be the congressional equivalent of destroying the village to save it.

"The president said he wanted to tear up the deal. He's now taking a step that would lead to tearing up the deal," said Rep. Peter Welch (D-Vt.), one of the key members who whipped support for the Iran deal in Congress when it was struck. He called Trump's move to kick the deal to Congress a "trap" and "a tactic intended to reach the president's goal of tearing the deal apart."