U.S. foreign policy has often been likened to an oil tanker. It can shift course, but major changes in direction happen slowly, if ever. But one prominent exception to this rule is now taking place: the U.S. foreign policy consensus on China, which has shifted rapidly in recent years and is still moving.

As part of his ongoing tirade against immigration, President Donald Trump has threatened to shut down the southern border completely. First, he said he would take action if Mexico doesn’t stop the flow of migrants; later, his demand was Mexico ending drug trafficking. Maybe it is both, though neither is feasible.