With Russian forces continuing to mass on Ukraine’s borders, hawkish officials and analysts are pushing a variation of the domino theory from the Cold War, claiming that a weak American response to the Kremlin in one theater will tempt another adversary, China, to take advantage of the U.S. a half a world away.

In the updated version, the U.S. defeat in Afghanistan, coupled with a successful Russian invasion of Ukraine, will embolden China to seize Taiwan. But linking the fate of Ukraine with that of Taiwan is almost certainly wrong: It misreads their respective strategic importance to Washington, as well as China’s strategy to bring Taiwan under Beijing’s control.

President Joe Biden has threatened Vladimir Putin with crippling economic sanctions if he orders the 100,000-plus Russian troops, tanks and self-propelled artillery on Ukraine’s borders to invade. But Biden has made it clear that U.S. support for Ukraine will be confined to defensive military…