President Donald Trump revealed Saturday the United States intends to withdraw from a 31-year-old nuclear weapons agreement with Russia, delivering a severe blow to the arms control regime that helped preserve peace since the Cold War.

“We’re going to terminate the agreement and we’re going to pull out,” Trump told reporters after a rally in Elko, Nevada, without indicating what the next steps might be.

The Intermediate-Range Nuclear Forces (INF) Treaty, first signed by President Ronald Reagan and Soviet Union leader Mikhail Gorbachev in December 1987, was the first and only nuclear arms control agreement that ever eliminated an entire class of nuclear weapons. The treaty forced the superpowers to scrap more than 2,600 missiles with ranges 310 to 3,420 miles — weapons considered destabilizing to the European continent because of their capability to launch a nuclear strike from anywhere without early warning.

U.S. intelligence first recognized Moscow’s potential violation of the agreement several years ago when the missile, the Novator 9M729, was still in its test phase. The Obama Administration worked unsuccessfully to persuade the Kremlin to stand down the program through diplomatic talks.

The Trump Administration, in contrast, directly confronted the violation by funding development of its own missile. The research is allowed under the INF, and only breaches the deal if that missile is ever tested or deployed. Aggressively responding to violations of treaties, launching new nuclear weapons programs and reminding the world about the power of the U.S. nuclear arsenal is Trump’s way of deterring others from expanding, or seeking, arsenals.

“Russia has violated the agreement,” Trump said. “They’ve been violating it for many years. And I don’t know why President Obama didn’t negotiate or pull out. And we’re not going to let them violate a nuclear agreement and go out and do weapons, and we’re not allowed to.”

Russia, for its part, has repeatedly denied it ever violated the INF. The Kremlin has instead insisted that the U.S. is the one that’s in defiance of the agreement, saying certain interceptors on American missile defense systems have offensive capabilities. The U.S. has dismissed Russia’s allegation as false and a red herring.

Regardless, National Security Advisor John Bolton will deliver the president’s decision to walk away from the INF to Moscow on Sunday during the first-stop of his upcoming trip through Russia, Azerbaijan, Armenia and Georgia. Bolton would not comment, but a senior Administration official said: “The United States and our allies have attempted to bring Russia back into full and verifiable compliance with INF. Despite our objections, Russia continues to produce and field prohibited cruise missiles and has ignored calls for transparency.”

Arms control experts worry about the second- and third-order consequences of tearing up a long-standing nuclear treaty. Jeffrey Lewis, a nuclear weapons analyst with the James Martin Center for Nonproliferation Studies in Monterey, Calif., said the U.S. has nothing to gain by walking away. “It’s a mistake,” he said. “Russia violated the treaty, but we’re going to take the blame for killing it? Why do Putin a favor?”

Lewis believes the U.S. will not deploy new missiles that would have been prohibited by INF, but Russia will. He says Moscow will step up the deployment of the Novator 9M729 or other formerly treaty-busting weapons.

The real risk will be borne by European allies, according to Kingston Reif, director for disarmament and threat reduction policy at the Arms Control Association, a think tank. “This removes all constraints on the production and fielding of Russia’s illegal missile, thereby increasing the threat to our allies in range of the missiles, leaves the United States holding the bag for the treaty’s demise, and creates another source of division between us.”

The whole basis for signing the INF three decades ago was the destabilizing nature of the weapons. The ballistic missiles, the Russian SS-20 and American Pershing II, could be driven on a mobile launcher into a remote area, blasted off and strike their targets in less than six minutes. The short timeline gave world leaders little time run for cover — let alone strategize about the right response.

Those facts haven’t changed. Europeans are not likely to want weapons like that on the continent. In a sign of those concerns, the North Atlantic Treaty Organization issued a statement earlier this year heralding the INF treaty as being “crucial to Euro-Atlantic security” and reducing the risk of conflict. “I don’t think the U.S. will try to ask anyone to deploy any INF systems on land – that would be a non-starter,” said Pavel Podvig, director of the Russian Nuclear Forces Project. “Russia will say that it was U.S. intent from the very beginning to pull out of the treaty and this is why it accused Russia of non-compliance … So, nothing good is coming out of this.”

Jon B. Wolfsthal, a nuclear weapons expert who worked on the National Security Council during the Obama Administration, said the INF withdrawal “poisons the well of nuclear stability” and will likely have a chilling effect on any possible nuclear arms deals between the U.S. and Russia in the future.

During the Cold War, a series of treaties between the U.S. and Soviet Union were designed to avoid miscalculation and keep communication channels open — even though Washington and Moscow were sworn adversaries. A number of those agreements have frayed in recent years but the last time that the U.S. unilaterally withdrew from a landmark nuclear arms control treaty was in 2002 when Washington left the Anti-Ballistic Missile Treaty and continued its expansion of ballistic missile defenses.

The effects of that decision was easily seen in March when Russian President Vladimir Putin unveiled his nation’s next generation of nuclear weapons, each engineered to slip behind America’s vast network of early warning and defense systems. In making the nationally televised speech to Russia’s Federal Assembly, Putin specifically stated the new arsenal serves as response to the U.S. government’s decision to abandon the Anti-Ballistic Missile Treaty.

However, the potential fallout from leaving the INF goes beyond Europe. Trump said China must also agree not to develop the missiles. This is a new development, considering China is not currently party to the INF. “We’ll have to develop those weapons — unless Russia comes to us, and China comes to us, and they all come to us and they say, ‘Let’s really get smart and let’s none of us develop those weapons.’ But if Russia is doing it and if China is doing it, and we’re adhering to the agreement, that’s unacceptable.”

If the U.S. decided to launch a nuclear strike on China, it has a range of ways to do so. In addition, the INF did not prohibit staunch allies, such as Japan or South Korea, from building ground-based missiles with the INF-busting range.

Navy Admiral Harry Harris, then-commander of U.S. Pacific Command, told the Senate Armed Services Committee in March that China was benefiting because of the United States’ adherence to the INF. “We are at a disadvantage with regard to China today in the sense that China has ground-based ballistic missiles that threaten our basing in the western Pacific and our ships,” he said.

Harris, who since retired and now serves as the American ambassador to South Korea, suggested the U.S. should start exploring ways to mitigate the threat: “We could do anything from one extreme — to pull out — to the other extreme — to do nothing — and I think we should look at ways to maximize our operational flexibility.”

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Write to W.J. Hennigan at william.hennigan@time.com.