British Ambassador to the United States Kim Darrouch, third from left, speaks during a discussion on “Europe and the Iran Deal” with French Ambassador to the United States Gérard Araud, second from left, German Ambassador to the United States Peter Wittig, right and European Union Ambassador to the United States David O’Sullivan, left, at the Atlantic Council in Washington on Sept. 25, 2017. (Nicholas Kamm/AFP/Getty Images)

More than any other issue that has threatened transatlantic cohesion this year, President Trump’s decision to decertify Iranian compliance with the nuclear deal could start a chain of events that would sharply divide the United States from its closest traditional allies in the world.

“After the Paris climate decision,” in which Trump withdrew the United States from a widely supported, painfully negotiated accord, “this could push multilateralism to the breaking point,” said a senior official from one of the three European signatories to the Iran deal.

None of the three — Britain, France and Germany — believes Iran is in violation, and each has said publicly it will not renegotiate the nuclear agreement.

U.S. imposition of sanctions affecting banks that even indirectly do business in Iran would doubtless influence those countries’ companies, they say, and would be considered an unfriendly act.

President Trump spoke about the agreement with Iran on their nuclear program when meeting with military leaders on Oct. 5. (The Washington Post)

“We will not follow the United States in reneging on our international obligations with this deal,” said a second official. “Not the E-3, nor the rest of the 28” members of the European Union.

Trump is expected to give a speech late next week announcing his decision and outlining the results of a months-long Iran policy review. People familiar with his thinking say he will not certify that Iran is honoring its commitments and will declare that sticking with the deal is no longer in the U.S. national interest.

Nothing will happen immediately, as the decision would be punted to Congress. The Senate could decide to restore pre-deal sanctions on Iran with a simple majority of 51, including a vote by Vice President Pence to break any tie.

In that case, Iran could call for a meeting of the majority-ruled committee of signatories and declare that the United States has violated the deal, an assertion with which the Europeans think they would be hard put to disagree. That would put them on the same side as two other signatories — China and Russia — that are sure to support Iran, leaving the United States as a minority of one.

“What do we do? What do we say?” asked the first European official, one of several from the signatory countries who spoke on the condition of anonymity to candidly discuss the sensitive diplomatic issue. “It would be a big crisis.”

The Europeans insist that everyone with whom they have spoken inside the Trump administration — except for Trump himself — has expressed opposition to decertification. But they have for some time considered his decision a foregone conclusion and have directed their attention to Congress, where even some Republicans who have long opposed the deal as deeply flawed worry that a reimposition of sanctions might make matters worse.

“We’re working the Hill a lot,” the first official said. “What we understand is that there is no inclination in the Senate to kill the deal by voting immediate sanctions. Staffers tell us that nothing is decided.

“But we’re convinced somebody like Cotton will go out with a bill,” said the official, referring to Sen. Tom Cotton (R-Ark.). “That will cause a crisis among the Republicans. . . . Nobody wants to appear to be defending Iran. Nobody wants to appear to be defending Obama.”

The White House has seemed to signal to Republicans that they can decide not to immediately reimpose sanctions, and Cotton himself, an outspoken hawk on Iran who met Thursday with Trump, said this week that he has “no intention right now to introduce . . . sanctions legislation.” While a law passed when the deal was done gives Congress 60 days to reimpose the sanctions lifted by the agreement with relative ease, lawmakers can take more time and pass a new sanctions law whenever they want.

“I’m not sure 60 days is enough,” Cotton said Tuesday at the Council on Foreign Relations, for the United States to practice “coercive diplomacy” to bend others to its will. It might, he said, take until spring but no longer.

“I hope we don’t have to coerce allies. I’d like to persuade allies,” Cotton said. “Many of them don’t require much persuasion, allies in the Middle East, for instance,” although they are not signatories to the deal. “But, ultimately, countries have to make a decision, if it comes to that. Do they want to deal with the United States’ $19 trillion economy, or do they want to deal with Iran’s economy . . . about the size of Maryland?”

Even if European political leaders are unpersuaded, he said, European businesses, vulnerable to U.S. sanctions if they continue dealing with Iran, may be. And if that does not work, Cotton said, “let there be no doubt about this point: If forced to take action, the United States has the ability to totally destroy Iran’s nuclear infrastructure. And if they choose to rebuild it, we could destroy it again, until they get the picture.”

Such comments infuriate the Europeans. “I would remind our American friends that when we started to impose sanctions, the United States did not have any trade with Iran . . . [and] we carried the burden” of financial losses, Gérard Araud, France’s ambassador to the United States, said last week at the Atlantic Council.

A Western diplomat in Zurich said the Europeans are contemplating reviving regulations the E.U. used to shield its companies and individuals from U.S. secondary sanctions in the 1990s. “Everyone’s looking at options,” the diplomat said.

Any deal without the United States would be “very fragile” in terms of keeping the incentive for Iran to uphold its side of the bargain, said a senior executive with a large multinational corporation. “It will also play to the hard-liners in Iran and help shift power back to them,” the executive said.

Long-standing Republican antipathy to the deal has come back to haunt its creators. Negotiators had envisioned a U.S. president who would justify staying in the arrangement as long as Iran lived up to its obligations, not a die-hard opponent who has branded the agreement an “embarrassment.” The 60-day, expedited “snapback” provision in U.S. law was designed to punish Iran quickly in the event it violated the deal and did not envision that the United States would breach it.

Europeans are frustrated with what they consider misperceptions about what the agreement says and what it was intended to do. While Trump and other critics say Iran got a $100 billion “payoff,” Europeans counter that the money belonged to Iran and was frozen in Western banks under sanctions. And although detractors say all of the deal’s restrictions on Iran’s nuclear program will be moot when some provisions of the arrangement expire in 2025, Iran will remain under the requirements of the Nuclear Non-Proliferation Treaty, which forbids weapons development.

And negotiators of the deal deliberately separated the nuclear program from their many complaints that Trump and others say are now reason to renegotiate or abrogate it — Iran’s development of ballistic missiles, its destabilization of the Middle East and its support for terrorism.

“We can speak with the administration about containing Iran’s malign influence,” the second European official said. “The question is: Does the U.S. have a strategy for that? Maybe they do. I don’t know.”

Erin Cunningham in Zurich contributed to this report.