A week that began with renewed threats of a trans-Atlantic trade war ended with the U.S. stock market finishing roughly where it began. The topsy-turvy path to Friday’s quiet close reminded investors of the many forces that have made markets’ record-breaking run in recent months feel more like a high-wire act. President Trump threatened additional tariffs on some of America’s longest-standing allies in a bid to acquire Greenland, and then promptly walked them back.