On foreign issues that directly affect domestic concerns, Mr. Trump pursues radical change. But on matters that are truly foreign, he is willing to adopt a traditional stance. What looks like inconsistency is actually an instinct deeply grounded in his worldview.

This explains the president’s withdrawal from the Trans-Pacific Partnership and his desire to renegotiate the North American Free Trade Agreement. Some charge that this is a betrayal of America’s decades-long commitment to a liberal global economic system. But Mr. Trump sees it as a domestic priority, a necessary shielding of American workers. Instead of sweeping, multicountry agreements, he has proposed bilateral trade pacts, beginning with Britain and possibly Japan.

On pure foreign policy, Mr. Trump has stayed the course for now. After initially questioning the relevance and utility of America’s main postwar alliances, he now seems committed to them. The president and Defense Secretary Jim Mattis have affirmed the mutual-defense agreements with Japan and South Korea. Mr. Mattis had tough words for NATO allies last week when urging increased military spending, but walking away seems a remote possibility.