Citing classified intelligence information, President Donald Trump revealed the U.S. government’s intention to withdraw from a landmark arms control treaty with Russia that has kept mid-range nuclear-tipped missiles off the European continent for three decades.

The reason, Trump said, was that Russia had violated the Intermediate-Range Nuclear Forces (INF) Treaty “for many years” by building, producing, and fielding prohibited cruise missiles despite repeated warnings from Washington.

Russia has denied any violation and has demanded proof from the United States to back up the claims. That information is secret, the U.S. said in response, and revealing it would compromise America’s spies capability to gather intelligence inside Russia. However, now that Trump is prepared to tear up the 31-year-old agreement, nuclear arms experts are calling for some of the evidence to be shared publicly in order to prove the Kremlin’s defiance to the world.

The 1987 INF treaty forced the U.S. and then-Soviet Union to scrap more than 2,600 missiles with ranges from 310 to 3,420 miles — weapons considered destabilizing to the European continent because of their capability to launch a nuclear strike without early warning. European allies have thus far been opposed to the United States’ withdrawal from the INF, while also demanding more transparency from Russia on its alleged offending missile, known as the Novator 9M729.

“We should make our case publicly,” said Andrew Weber, who spent 30 years on nuclear weapons issues in the U.S. State and Defense departments before retiring in 2015. “It would certainly be helpful. I’m not sure why they haven’t already done so. They could make a declassified disclosure in a way that would protect sources and methods.”

The burden of proof — in the form of photos, video, or other evidence —becomes all that more important with a leader like Trump, who is known to make broad and controversial claims without offering much evidence, the analysts say.

The allegation that Russia is out of INF compliance is not new. Since 2014, the U.S. State Department has stated Moscow’s violation in its lengthy annual report, “Adherence to and Compliance with Arms Control, Nonproliferation, and Disarmament Agreements and Commitments.” Several years prior to that disclosure, officials said U.S. intelligence agencies found evidence of the missile when it was still in test phase.

Over all that time, the Americans’ proof of the violation has been secret. Nothing has been published about the weapon or its capabilities. The Obama Administration opted to work behind the scenes to persuade the Kremlin to stand down the program through diplomatic talks.

Underwhelmed by that tactic, the Trump Administration went a little further by publicly revealing the name of the missile as the 9M729 in December 2017. The disclosure later prompted Russia to admit for the first time that it did, indeed, possess a new type of ground-launched missile, according to NATO Secretary General Jens Stoltenberg. (The weapon was derisively nicknamed the SSC-8 “Screwdriver” by NATO analysts because “Russia used it to screw us,” officials say.)

The U.S. has routinely briefed NATO allies on the intelligence about the missile, but there are limits on how much information can be shared. There are tell-tale signs that some U.S. allies remain unconvinced by the evidence.

Hans Kristensen, a nuclear weapons expert at the Federation of American Scientists, pointed to NATO’s July summit declaration that said there were “doubts” about Russia’s INF compliance, instead of certainty. “It did not state NATO allies are convinced about the facts, only that Russia’s lack on answers makes a violation the most likely assessment,” he said. “U.S. officials still insist that the launcher and deployment locations are secrets. But releasing that would further increase pressure on Russia. Ironically, the details the U.S. have been showing Russia are probably more extensive than what it has been willing to tell the public.”

John Bolton, Trump’s national security advisor, is currently in Moscow where he is set to inform Russian leaders of the United States’ intention to leave INF. Under the terms of the agreement, the U.S. must give Russia a six-month notice before formal withdrawal.

At the White House on Monday, Trump told reporters that he plans to leave the INF and expand the American nuclear arsenal with the hopes it will coerce Russia into compliance. “We’ll build it up until they come to their senses,” he said. “When they do, then we’ll all be smart, and we’ll all stop. And by the way not only stop, we’ll reduce, which I would love to do. But right now, they have not adhered to the agreement.”

When asked whether he had spoken to Putin about his decision, Trump replied: “I don’t have to speak. I’m terminating the agreement because they violated the agreement. I’m terminating the agreement.”

Philip Breedlove, a retired U.S. Air Force general who commanded all NATO forces in Europe from 2013 to 2016, says the U.S. has a responsibility to explain to the American public what’s at stake by leaving the INF. The electorate also needs to know how, when, and where Russia violated this agreement, he said.

”We have to get the story out that Russia has abrogated this treaty already and that we either need to respond or bring them back into compliance, because I don’t think Joe and Sally Sixpack in America understand that,” Breedlove said during a teleconference organized by the Atlantic Council, a Washington think tank. “We need people to understand that this more than just, ‘They have nukes and we have nukes.’”

Withdrawing from the INF could have broader implications on other arms control agreements, such as the New Strategic Arms Reduction Treaty, or New START, which is set to expire on Feb. 5, 2021. The linchpin agreement limits each side to 1,550 deployed nuclear warheads and 700 deployed heavy bombers and ballistic missiles. It also includes a thorough monitoring and verification regime to help ensure compliance. If New START sunsets, it will be the first time in the effort to limit the strategic stockpiles in the U.S. and Russia since 1972.

Ellen Tauscher, a former undersecretary of State for arms control and international security from 2009 to 2012, said the Trump Administration must be mindful of the risks before ripping up the INF. “The Administration is on a terrible path of for getting the United States’ blamed for this when it’s actually the Russians’ (fault),” she said during the teleconference. “We have not worked with our allies; we have not prepped people for what this means.”

In tit-for-tat language reminiscent of the Cold War, Russian state media reported Monday that if the U.S. withdraws from the INF, Moscow will “take measures on ensuring its own security.”

Get our Politics Newsletter. The headlines out of Washington never seem to slow. Subscribe to The D.C. Brief to make sense of what matters most. Please enter a valid email address. Sign Up Now Check the box if you do not wish to receive promotional offers via email from TIME. You can unsubscribe at any time. By signing up you are agreeing to our Terms of Use and Privacy Policy . This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply. Thank you! For your security, we've sent a confirmation email to the address you entered. Click the link to confirm your subscription and begin receiving our newsletters. If you don't get the confirmation within 10 minutes, please check your spam folder.

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