Director of National Intelligence Daniel Coats at the White House on Aug. 2 in Washington. (Jabin Botsford/The Washington Post)

THE TRUMP administration has now served notice that, as Secretary of State Mike Pompeo put it, the United States will no longer “bury our head in the sand” about Russia’s violation of the Intermediate-Range Nuclear Forces Treaty, a 1987 pact that eliminated an entire class of nuclear-armed missiles. Mr. Pompeo said the United States won’t adhere to the treaty unless Russia comes into compliance within 60 days. Russia’s violation is real, but walking away from the treaty will only make matters worse. Who is burying their heads in the sand?

The treaty, signed by President Ronald Reagan and Soviet leader Mikhail Gorbachev, bans ground-based missiles, both ballistic and cruise, both nuclear and nonnuclear, with ranges between 500 and 5,500 kilometers. It marked a turning point in the Cold War, the reversal of a deadly competition that began in the 1970s with the Soviet deployment of SS-20 missiles aimed at Western Europe and followed by the deployment of U.S. Pershing II and ground-launched cruise missiles in 1983. Negotiations eventually led to a treaty with unprecedented, intrusive on-site verification measures, perhaps the most important ever negotiated in nuclear arms control. Both countries sent teams to see the other slice up the missiles.

In the 2000s, Russia under President Vladimir Putin began to slice up the treaty instead. Russia covertly began developing a cruise missile, known as the 9M729, that was outlawed by the agreement. The U.S. director of national intelligence, Daniel Coats, deserves credit for revealing key details late last month about how the violation happened and how it was discovered during President Barack Obama’s administration. He said Russia’s Novator developed the missile, and by 2015 had finished comprehensive flight tests from both fixed and mobile launchers. The tests were cleverly designed, he reported, to disguise their true nature and the missile’s capability. The treaty permits certain tests of a legal missile from a fixed launcher as long as the weapon would then be deployed on ships or planes, not on the ground. So Russia initially tested the 9M729 from such a fixed launcher but at prohibited ranges greater than 500 kilometers, then from a mobile launcher at a lesser distance. With these tests taken together, and also by mixing the tests with other, legal ones, Russia tried to cover its tracks and eventually deployed “multiple battalions” of a weapon banned under the treaty, Mr. Coats said. The missile poses “a direct conventional and nuclear threat against most of Europe and parts of Asia,” he declared. When confronted, Russia steadfastly denied it had violated the treaty and rebuffed attempts to resolve the issue.

The administration is right to confront the issue, but not to just walk away. President Trump has not exhausted all the options with Mr. Putin, and U.S. allies in Europe are not sanguine about facing Russian missiles again. Mr. Trump periodically muses about how he would like to do something about “a major and uncontrollable Arms Race.” Abandoning the INF treaty would mean restarting an arms race.