Last Wednesday, standing at a podium in the White House Rose Garden, the president of the United States threw the world’s economy into turmoil. Having declared that America’s trade deficit represented a bona fide “emergency,” President Trump revealed a completely rewritten federal tariff regime. The result of these alterations was an increase in protectionist barriers that exceeded even the infamous Smoot-Hawley law in its scope. For two days, the stock market responded to this move by diving sharply downward. Monday morning, after a false report that the president was planning to endorse a 90-day pause in implementation, there was a...