If Biden doesn’t deter Putin from “rash action” on Ukraine, “then the alliance will fragment,” Niblett said. “This is why the Ukraine crisis is the test.” Other nations have been flexing muscles and pushing the limits for their own misadventures. On Sunday, China flew thirty-nine warplanes near the disputed island of Taiwan, forcing Taiwan to scramble its own air fleet. Beijing has claimed the island since the two nations split, in 1949. “The nightmare scenario is war on two fronts—Ukraine and Taiwan blowing up at the same time,” Mark Leonard, the co-founder and director of the European Council on Foreign Relations, told me. This month, North Korea has carried out five ballistic-missile tests, and Kim Jong Un has threatened to end the moratorium on long-range missile and nuclear tests. Since December, Iran’s new hard-line government has played hardball in talks, in Vienna, with the world’s six major powers about how to get the U.S. and Iran back into the 2015 nuclear deal. Tehran is now estimated to be only three weeks away from having enough enriched uranium to fuel its first nuclear bomb.

Biden’s showdown with Russia over Ukraine could affect U.S. interests around the world. The stakes include the fate of peace in Europe and the power of the Western alliance and nato, the world’s mightiest military coalition. More broadly, the crisis is about the balance of power between democrats and autocrats worldwide. It’s about “whether nations—big or small, powerful or weak—are sovereign and can’t be forced into a larger power’s sphere by coercion,” Taylor said.

If Biden can’t persuade Russia to accept Ukraine as a sovereign state allowed to make its own decisions on security, Niblett said, America’s allies in Asia and the Middle East may feel they can no longer trust U.S. commitments to their security, leading them to seek accommodations with China and other adversaries of the United States.