President Donald Trump put America at greater risk by withdrawing from the Iran nuclear deal.

While the multilateral pact was imperfect, it prevented Iran from developing a nuclear weapon. Multiple International Atomic Energy Agency (IAEA) inspections confirmed compliance, a fact acknowledged by the U.S. and others party to the deal (technically, the Joint Comprehensive Plan of Action, or JCPOA). Five of these nations — Russia, China, and stalwart allies France, Germany and the United Kingdom — signaled that they would honor it even if the U.S. broke its pledge.

Iran has not made its intentions known. Tehran may uphold its end of the bargain, at least for now. But it’s possible, even probable, that hard-liners ascendant because of Trump’s decision will urge the theocracy to push out IAEA inspectors and push ahead in developing a nuclear weapon. They might also push the Iranian government to further menace the Mideast, just as it has done by backing the Assad regime in Syria, Hezbollah in Lebanon, the Houthis in Yemen and more radical factions in Iraq, who may see a surge in upcoming parliamentary elections.

Iran’s backing of these bad actors and its direct threat to Israel are key reasons why it’s imperative that Iran not develop a nuclear weapon. The JCPOA was accomplishing this. Trump not only recklessly rejected this effective tool without any alternative, he weakened if not destroyed the multinational consensus that coalesced around sanctions that were tough enough to drive Iran to the negotiating table in the first place.

Now, the U.S. is isolated — just as it is by Trump’s rejection of the Paris climate accord and the Trans-Pacific Partnership (and maybe even NAFTA) free-trade agreements, which were scrapped (or endangered, in the case of NAFTA) without fully developed alternatives.

Trump reeled off his reasons when he addressed the nation on Tuesday, but his true motivations are uncertain. Perhaps to placate a base that has stuck with him, or to respond to new hawkish, hard-line advisers such as Secretary of State Mike Pompeo and National Security Adviser John Bolton. Maybe Trump acted in response to Sunni Gulf allies who believe that they are in an existential struggle against Shiite Iran, or to Israeli Prime Minister Benjamin Netanyahu, who has long tried to undermine the deal despite much of Israel’s military establishment backing it. Or even as the latest rebuke of former President Barack Obama.

Regardless of motive, the result is that the president alienated allies and proved untrustworthy as he gets set to negotiate with North Korea, a nation that actually has a nuclear arsenal.

Trump is ultimately responsible for this gamble and the uncertain aftermath, but he was enabled by compliant, complicit congressional Republicans and a conservative media echo chamber that is damaging America’s standing in the world. Responsible politicians and citizens should urge a return to multilateral diplomacy instead of unilateral actions that increase the chance of war.