The one biggish economy that’s foundering is the one Trump has celebrated: Brexiting Britain. There, populists are proving politically incompetent and economically harmful. British growth, which sputtered in at an annualized rate of 1.2 percent in the second quarter, is the lowest among the major economies. The pound is weak, even against the limping dollar. Inflation has jumped. Perhaps it is time for Trump to take stock of the world and ask himself: Who’s looking great — and who is not?