It’s become conventional to describe Donald Trump’s foreign policy as incoherent or contradictory — hell, I’ve almost certainly done it myself. One could argue that those labels fit all too well at the end of a week when Trump has “unleashed global chaos” (to quote a Friday report in the Guardian) with a long list of varying tariff rates inflicted on virtually every country in the world. But that conventional explanation is basically wrong, and leaves the curators of mainstream foreign-policy wisdom flopping back and forth trying to untangle the Trump decisions they like from the ones they hate. Trump’s...