If a cold war is breaking out, why now? Although the United States and Soviet Union had different political and economic systems, their antagonism centered on a specific dispute: the future of postwar Germany. No single sticking point cleaves America and China today. Nor are ideological differences as acute. China no longer seeks the universal triumph of communism, and the United States is moving away from exporting democracy. Perhaps this should reassure us that relations will not descend into open conflict. Or perhaps the extent to which they already have indicates that a darker logic is at work.

The anti-China turn of the past year has been triggered more by American anxieties than by Chinese actions. The latter, by and large, are not new. What is new is President Trump, who has both introduced a distinctive animosity toward China and provoked the American political class to seek a new purpose for America’s global leadership.

Mr. Trump, a xenophobe, has for decades placed the blame for America’s problems on non-Western powers, first Japan in the 1980s and then China. His administration reflects this worldview. Ms. Skinner calls China a “really different civilization.” “This is the first time that we will have a great power competitor that is not Caucasian,” she has said, disregarding imperial Japan and Orientalized portrayals of the Soviets. Her point is nonetheless significant: If the original Cold War pitted liberal capitalist democracy against state communism, its successor may promise brute power politics wrapped around a clash of civilizations. No wonder Steve Bannon, doyen of the alt-right and Mr. Trump’s former counselor, thunders that China poses “the greatest existential threat ever faced by the United States.”

Mr. Trump has mattered in a second way. His election caused foreign-policy mandarins to panic over “isolationism” and scramble to save American power. After banding together to defend the “liberal world order,” they have arrived at a surer solution: contain China. Beijing presents an ideal foil — a major adversary that justifies globe-spanning responses but doesn’t pose much immediate threat of war. On Capitol Hill, getting tough on China ranks among the few causes that unite Democrats and Republicans. Economic nationalists imagine jobs returning to America, free-traders think pressure will open up China, and everyone gets to sound tough on defense. Today’s climate reminds Senator Chris Coons of “the 1950s when there was no downside, politically, to being anti-Soviet.”

That is not to say that China hawks are insincere or irrational. They are right that China’s rise inherently threatens American interests — so long as America defines its interests as maintaining global dominance everywhere and forever. For advocates of the “United States-led liberal order,” what really counts is American leadership, even when supplied by Mr. Trump. In this respect, too, his presidency is clarifying.