The past few weeks have witnessed a kind of turning point in the Trump administration’s foreign policy, as the president cycles back to some of his original campaign themes. These include the continued pulverization of ISIS, hardened sanctions against Iran, repeat calls for increased allied military spending, summit meetings with Vladimir Putin and Kim Jong-un, an American tariff campaign against China, and similar tariff campaigns against U.S. allies. Some of these directions are warranted, and even welcome. But all require careful monitoring, and some could cause problems. Current trade wars with U.S. allies, for example, threaten to undermine the rest of the president’s stated foreign-policy agenda, along with a good deal more.