WASHINGTON (Reuters) - Republicans in the U.S. Congress, long the staunchest opponents of the Iran nuclear deal, may be the best hope for preserving it if President Donald Trump declines on Friday to certify that Tehran is complying with the pact.

Every Republican in Congress opposed the international accord reached under Democratic former President Barack Obama two years ago. Joined by several Democrats, they nearly passed legislation to kill the deal in which Iran agreed to curb its disputed nuclear program in exchange for sanctions relief.

However, with the agreement in place and strongly supported by co-signers Britain, France, Germany, Russia and China, many Republicans who still abhor the pact nevertheless do not want to blow it up for fear that doing so would erode U.S. credibility. They want to find other ways to clamp down on Tehran.

Meeting with officials from the Trump and Obama administrations, European diplomats and among themselves, they have been preparing strategies to save it, including pushing for tougher inspections, changing the law requiring Trump to certify Tehran’s compliance and setting new sanctions over Iran’s non-nuclear activities.

“As flawed as the deal is, I believe we must enforce the hell out of it,” Representative Ed Royce, the Republican chairman of the House Foreign Affairs Committee, said on Wednesday.

On Friday, Trump is expected to unveil a broad strategy for Iran, including announcing that he will decertify the agreement ahead of an Oct. 15 deadline, although he could always change his mind.

If the Republican president goes ahead, that would open a 60-day window in which Congress could reimpose sanctions, a step toward an unraveling of the deal.

FILE PHOTO: U.S. President Donald Trump addresses Joint Session of Congress - Washington, U.S. - 28/02/17 - Republicans applaud as U.S. President Donald Trump addresses the U.S. Congress. REUTERS/Kevin Lamarque

PRESSURE ON REPUBLICAN LAWMAKERS

However, Trump is not expected to call on lawmakers to revive those sanctions. If he stops short of recommending that, it gives Republicans room to stand pat for now.

Daniel Kurtzer, a former U.S. ambassador to Israel who is now a professor at Princeton University, said the political pressure could be intense. “There will be an onslaught of phone calls and letters and visits to senators to ‘do something’ about Iran,” he said.

Israeli Prime Minister Benjamin Netanyahu has urged Washington to either fix the Iran deal or “nix it.”

On Wednesday, H.R. McMaster, Trump’s national security adviser, discussed Iran with the Republican chairmen of House of Representatives national security committees. On Thursday, intelligence officials scheduled a classified briefing for members of the House Foreign Affairs Committee.

Senate Foreign Relations Committee Chairman Bob Corker, a key player in the Iran debate, has suggested changing the Iran Review Act he co-authored to eliminate the requirement that Trump recertify Iran’s compliance with the deal every 90 days, several congressional sources said.

Trump, who pledged during his campaign to rip up the Iran deal, has recertified it twice since taking office in January and hates having to do so.

A Twitter feud that erupted this week between Trump and Corker could complicate the efforts by the influential Republican to broker a deal that would likely require both Democratic and Republican support.

“Congress and the administration need to be on the same page, and a major breakdown in the working relationship between one of the very few key Republicans on the Hill who works with Democrats and the president on Iran policy bodes very poorly,” said Elizabeth Rosenberg, a former Treasury Department official now at the Center for a New American Security.

To win over some conservative Republicans and Iran hawks, Corker and other leaders are considering proposing sanctions on Iran’s non-nuclear activities and broader inspections, particularly of Iranian military facilities.

On Thursday, the House Foreign Affairs Committee approved sanctions targeting Iran’s ballistic missiles development. It could come up for a vote in the full House well before the end of the 60 days Congress has to react to Trump’s announcement.