Defying most of the worldinfo-icon, President Trumpinfo-icon announced on Friday that the landmark 2015 Iraninfo-icon nuclear deal is no longer in the U.S. interest, and took the first step toward unravelling it. The accord--brokered jointly with Britaininfo-icon, Chinainfo-icon, Franceinfo-icon, Germanyinfo-icon, and Russiainfo-icon, during two years of often tortuous diplomacy--is the most significant agreement stemming proliferation of the world's deadliest weapon in more than a quarter century. It now faces a precarious future--with the United Statesinfo-icon, not Iran, shaping up as the first country to violate its terms.

"We will not continue down the path whose predictable conclusion is more violence, more terror, and the very real threat of Iran's nuclear breakout," Trump said in an early-afternoon address.

The unveiling of the Trump Administration's long-awaited Iran policy--after nine months of contentious internal debate--is somewhat of a compromise. The President did not formally pull out of the deal, despite his description of it, on Friday, as "one of the worst and most one-sided transactions the United States has ever entered into." But he is now refusing to certify--as required every ninety days by U.S. law--that Iran has fully complied, even though his own Administration acknowledges that Tehraninfo-icon has met all its obligations for two years. International inspectors with the International Atomic Energy Agency have also reported eight times, most recently in August, that Tehran is obeying the terms.

Trump instead based his total reversal of U.S. policy on grounds that the Islamic Republic is in violation of the "spirit" of the accord. "The Iran deal was supposed to contribute to 'regional and international peace and security.' Yet," Trump said, "the Iranian regime continues to fuel conflictinfo-icon, terror, and turmoil throughout the Middle Eastinfo-icon and beyond." The reference to peace comes from a single sentence in the preface of a hundred-and-fifty-nine-page document--and is not central to any aspect of what is purely an arms-control agreement.

Trump's decision to decertify Iran--after twice certifying its compliance this year--now punts action to Congress. It has sixty days to decide whether to re-impose punitive sanctions that were originally lifted as the incentive for Iran to surrender most of its nuclear program. If Congress re-imposes sanctions, the United States will be violating its obligations under the Iran deal.

As an alternative, Trump called on Congress to consider broader legislation addressing "flaws" in the deal--with specific triggers that would automatically re-impose U.S. sanctions. But the so-called flaws Trump cited cover issues--such as Iran's missileinfo-icon program--outside the deal. A White House fact sheet also cited Iran's material support for terrorism, role in the Syrian regime's atrocities, hostility toward Israelinfo-icon, threats to freedom of navigation in the Persian Gulfinfo-icon, "grievous" human-rights abuses, detention of American citizens "on specious charges," and cyberattacks on Israeli and U.S. allies in the Middle East.

The President called on other countries in the accord to adopt similar action--or else, he said. "In the event we are not able to reach a solution working with Congress and our allies, then the agreement will be terminated," the President said, in an address from the White House Diplomatic Reception Room. "Our participation can be cancelled by me, as President, at any time." Trump's policy basically offers fix-or-nix options.

Whether the White House can muster sixty votes to pass legislation now being crafted by the Republican senators Tom Cotton and Bob Corker is questionable. The bill would reportedly alter the so-called sunset timelines that allow Iran to resume some activities over set times. But the bill would require eight Democrats to pass.

Some Democrats who questioned the deal brokered during the Obama Administration now oppose scrapping it. "I think I speak for a lot of usinfo-icon who opposed the agreement. We thought it was the wrong decision," Senator Ben Cardin, of Maryland, the ranking member of the Senate Foreign Relations Committee, told reporters recently. "Once it was entered into, once it was implemented, we want to see it enforced. We don't want to see the United States violate it."

Trump's long-anticipated Iran policy has sweeping implications far beyond Iran. It creates tensions with allies, and China and Russia, as well, that could have a major impact on other global crises. It undermines diplomacy to resolve the escalating showdown with North Koreainfo-icon. It weakens U.S. credibility on arms control--and, for that matter, international agreements on any issue. It threatens U.S. efforts to defuse other flash points in the Middle East. And it risks escalating tensions with Iran--and the first tentative engagement on regional issues, after almost four decades of hostility.

The world's major powers quickly spurned Trump's appeal to amend or renegotiate the Iran accord. Federica Mogherini, the foreign-policy chief of the European Unioninfo-icon, who hosted the two-year talks, said on Friday that the agreement "does not belong to any single country and it is not up to any single country to terminate it."

In a joint statement on Friday, the leaders of Britain, France, and Germany expressed alarm at Trump's decision and reaffirmed their total commitment to the Iran deal. "Preserving the J.C.P.O.A."--the Joint Comprehensive Plan of Action--"is in our shared national security interest," Prime Minister Theresa May, President Emmanuel Macron, and Chancellor Angela Merkel said. "The nuclear deal was the culmination of thirteen years of diplomacy and was a major step towards ensuring that Iran's nuclear program is not diverted for military purposes." They noted that the deal was "unanimously endorsed" by the U.N. Security Council, and appealed to the Administration and Congress to "consider the implications to the security of the United States and its allies before taking any steps that might undermine the J.C.P.O.A."

The I.A.E.A. director general, Yukiya Amano, who oversees the inspections process, challenged some of Trump's assertions. Among them was an allegation that Tehran has prevented I.A.E.A. weaponsinfo-icon inspectors from entering military bases. "So far, the IAEA has had access to all locations it needed to visit," Amano said in a statement. "At present, Iran is subject to the world's most robust nuclear verification regime."

The former Secretary of State John Kerry, who led U.S. diplomacy with Iran, called Trump's decision "dangerous," and warned that it creates an international crisis. It's a reckless abandonment of facts in favor of ego and ideology from a President who would rather play a high-stakes game of chicken with Congress and with Iran than admit that the nuclear agreement is working," he said in a statement on Friday. "I strongly hope that the other six signatories will prove to the world what responsible behavior is, and adhere to this agreement--no matter what false accusations and contrived provocations are put forward by President Trump."

Trump's new Iran policy includes sweeping new sanctions on the Revolutionary Guard Corps and its elite Quds Force, as well as all its agents and affiliates. The move was partly designed to discourage foreign businesses and banks from reengaging with Iran now that international sanctions have been lifted by the United Nationsinfo-icon. "We urge the private sector to recognize that the IRGC permeates much of the Iranian economyinfo-icon, and those who transact with IRGC-controlled companies do so at great risk," Treasury Secretary Steven T. Mnuchin said in a statement.

For Iran, the return of foreign businessinfo-icon, trade, and investment is the core barometer of whether the deal was worth it. Last month, the Iranian foreign minister, Mohammad Javad Zarif, told me that Iran might be able to tolerate a U.S. decision not to certify as long as new sanctions weren't imposed and other countries continued to engage with Iran, particularly economically.

After Trump's address, the Iranian President, Hassan Rouhani, went on national television on Friday night to chastise Trump. The speech, Rouhani said, "contained nothing but expletives and a pile of delusional allegations against the Iranian nation." Rouhani, who was first elected in 2013, on a platform of ending the nuclear standoff, noted that Europe is now siding with Iran over the deal. "Americainfo-icon is now more than ever isolated," he said. "We will not expect anything else from you from now on. With your incorrect words, you made us more united than ever."