Donald Trump has repeatedly said that his move to impose wide-ranging tariffs is based on the simple concept of reciprocity: The U.S. should put the same conditions on imports from other countries that they impose on our goods through tariffs and other trade barriers. But the tariff scheme he announced isn’t reciprocal and isn’t based on measuring foreign trade barriers. Instead, it simply measures bilateral trade deficits and comes up with tariff numbers from there. Those are two very different things, and could be one reason why global financial markets are reacting so badly. The upshot is that, in the...