Military strategists know a battle can begin in one theater but quickly move into another. Similarly, what begins as a trade war can evolve into something bigger. It’s a truth worth remembering as the United States imposes substantially higher tariffs on our trading partners, who have the ability to respond in unanticipated ways.

Conversely, China exports more than it imports, runs more modest national government deficits and enjoys a current account surplus of about 2 to 4% of its GDP. Without reducing the federal deficit or putting the skids on U.S. investment and growth, Mr. Trump can’t reduce the trade deficit with just tariffs.