U.S. President Donald Trump said he intends to pull the U.S. out of a landmark 1987 treaty with Russia that rolled back ground-launched intermediate-range missiles in and aimed at Western Europe. The U.S. says Russia has violated the treaty, a charge Russia denies and turns back on the U.S. The Trump administration is poised to suspend the deal, called the Intermediate-Range Nuclear Forces treaty, as soon as Feb. 2. Its termination could revive the nuclear arms race in Europe and spur one in Asia.

1. What is the INF treaty?

The treaty, signed in December 1987 by U.S. President Ronald Reagan and Soviet leader Mikhail Gorbachev, was a high point for superpower arms-control efforts. It was preceded by a spiraling arms race: In response to Soviet deployments of SS-20 intermediate-range nuclear missiles that could strike Western Europe in the late 1970s, the U.S. put missiles of its own in West Germany, Italy and the U.K. After years of unproductive talks between the two sides on limiting the weapons, Reagan and Gorbachev reached agreement to eliminate them entirely. The INF treaty, which has no expiration date, called for both sides to destroy and never deploy again ground-based ballistic and cruise missiles with a range of 500-5,500 kilometers (300-3,500 miles), either nuclear or conventional. The pact allows similar weapons fired from ships or aircraft. A total of 2,692 missiles were destroyed by 1991 under the treaty, according to the U.S. State Department.

2. Why does Trump want to pull out?

The U.S. says the Russians haven’t been following the rules. The U.S. alleged in 2014 that Russia had tested a weapon, the 9M729 ground-launched cruise missile, at a range that fell under the treaty. In 2017, the U.S. said Russia had deployed that weapon. Then last October, NATO declared that Russia was in violation of the treaty. U.S. Secretary of State Michael Pompeo in early December said the U.S. was giving Russia until Feb. 2 to get back in compliance. Trump’s national security adviser John Bolton has called the INF treaty outdated and said it doesn’t address the rising threat from China, whose deployment of intermediate-range missiles is not bound by the accord.

3. What does Russia say?

Russia has said the relevant missile was never tested at distances banned under the agreement and has called on the U.S. to show proof of a violation. Russia also has accused the U.S. of breaching the treaty with its missile-defense systems in Europe, a charge Washington rejects.

4. What would happen without the treaty?

If the U.S. pulls out, Russia could go ahead with further deployment of the missiles that allegedly violate the treaty. The U.S. is already developing a weapon of its own to counter it, raising the possibility of a repeat of the Cold War-era arms race in Europe. The demise of the treaty would also free the U.S. to deploy mid-range nuclear weapons to counter China’s deployment of such arms, potentially escalating tensions in Asia. Trump has said that in general the U.S. “must greatly strengthen and expand its nuclear capability.”

5. How have other countries responded?

Trump’s threat to withdraw has caused jitters in Germany, a country that would be ground zero in a nuclear war in Europe and was at the front line of superpower confrontation during the Cold War. French President Emmanuel Macron said he has stressed to Trump the “importance of this treaty for the European security and its strategic balance.” China, wary of a new U.S. weapons buildup, said a pullout would have “multiple negative effects.”

6. Could diplomacy still save the pact?

The U.S. and Russia have had several rounds of discussions on the alleged violations since at least 2014, but without progress. Trump has said he would consider a new pact that included China, but officials there have shown no desire to join a treaty that would ban a large part of their nuclear arsenal. In the event the U.S. quits the treaty altogether, the six months required notice could allow time for diplomacy to save the deal, according to North Atlantic Treaty Organization chief Jens Stoltenberg.

7. Are other major arms-control deals under threat?

If the U.S. pulls out of the INF treaty, the only remaining pact regulating the world’s two biggest nuclear arsenals would be an agreement that expires in 2021. New START, signed in 2010 by then-Presidents Barack Obama and Dmitry Medvedev, sets limits on overall totals for nuclear weapons for each side. The treaty can be extended for five years if both sides agree. No talks have begun on prolonging the deal.