When President Donald Trump has talked about the need for higher tariffs on imports of foreign goods because of a decline in American manufacturing, he has often made the claim that “90,000 plants and factories” in the U.S. closed after the North American Free Trade Agreement with Canada and Mexico took effect in 1994. But that figure is questionable, and experts say other factors, such as automation, had more to do with the large decline in U.S. manufacturing jobs than trade. Data from the...