Bloomberg | Mark Niquette: The time is at hand for President Donald Trump to decide whether the U.S. remains in the Iran nuclear deal, and interested parties are making their final pitches.

Israeli Prime Minister Benjamin Netanyahu said Sunday that the 2015 accord is fatally flawed and must be “fully fixed or nixed” to stop Iranian aggression sooner than later. His comments came as Iranian President Hassan Rouhani warned that the U.S. would face “historic” regret if it pulled out.

Britain’s Foreign Secretary Boris Johnson meets in Washington this week with Vice President Mike Pence, National Security Adviser John Bolton, and other administration and Congressional officials to try to salvage the pact. His arrival follows recent visits by French President Emmanuel Macron and German Chancellor Angela Merkel.

Representative Mac Thornberry, a conservative Republican, said Sunday he “would counsel against” Trump leaving the deal. Still, House Majority Leader Kevin McCarthy said he’s “very comfortable” that the president is standing up to Iran.

Trump faces a May 12 deadline to decide, and has recently refused to reveal what he’ll do. While the president has repeatedly called the accord a bad deal for the U.S., and Trump lawyer Rudy Giuliani said Saturday he expectsit to be torn up, the president also said last week that his antipathy “doesn’t mean I wouldn’t negotiate a new agreement.”

Speaking to reporters on Sunday, Netanyahu said the agreement fails to address potential weaponization of Iran’s nuclear knowledge, imposing only temporary limits on uranium enrichment.

“I say that a deal that enables Iran to keep and hide all its nuclear weapons know-how is a terrible deal,” said Netanyahu, who’s warned for decades about Iran’s nuclear ambitions. The agreement must be “either fully fixed or fully nixed” because otherwise, “you will end up with Iran with a nuclear arsenal in a very short time,” he said.

Macron reiterated Sunday that he wants to maintain the Iranian nuclear accord, while “complementing” it with talks on Tehran’s ballistic missile program and regional activities, according to an interview he gave to Le Journal du Dimanche.

Iran, however, has ruled out new talks, calling the current agreement “non-negotiable.”

Rouhani, addressing crowds at a rally Sunday in the northeastern city of Sabzevar, said the U.S. has “always sought to sow intrigue against Iran” and would be making a huge mistake by exiting the agreement.

“If it wants to leave the nuclear deal, it will quickly see that this decision will be a regret of historic proportions,” Rouhani said.

U.S. negotiators have been meeting with allies France, the U.K. and Germany trying to reach a consensus on side agreements responding to U.S. concerns about the deal rather than scuttling it.

“I am sure of one thing: every available alternative is worse,” the U.K..’s Johnson said in column published by the New York Times on Sunday as he arrived in Washington for meetings on the deal. “The wisest course would be to improve the handcuffs rather than break them.”

‘A Few Days Left’

U.K. officials think “we can find some language, produce some action that meets” Trump’s concerns about the deal, Kim Darroch, the British ambassador to the U.S., said on CBS’s “Face the Nation” on Sunday.

“We haven’t got there yet,” Darroch said. “We have a few days left to see if we can find our way through.”

Thornberry of Texas, chairman of the House Armed Services Committee, suggested on “Fox News Sunday” that perhaps the president could delay his deadline so the U.K. and France can pursue the idea of new negotiations to strengthen the agreement.

By leaving the deal, the U.S. would lose visibility to what Iran is doing, Thornberry said. Iran promised to redesign, convert, and reduce its nuclear facilities while accepting inspections in return for an end to all nuclear-related economic sanctions, boosting oil revenue and regaining frozen assets.

“I thought it was a bad deal,” he said. “But the key question is, ‘OK, now we are where we are, what happens next if the U.S. pulls out?’”

But another leading Republican said Sunday that Trump is taking the right approach.

“It’s time someone stands up to them,” McCarthy, a California Republican, said on Fox’s “Sunday Morning Futures.” “That was a bad deal to start with, and history will show that was the wrong agreement, and I’m thankful that the president is looking at all options.”

— With assistance by Michael Arnold, David Wainer, Golnar Motevalli, Ben Brody, Alan Bjerga, Gregory Viscusi, and Nick Wadhams