Donald Trump and Angela Merkel now agree about the main issues in U.S.-German relations. “The times in which we could rely fully on others — they are a way past us,” Merkel told a beer-tent rally of her political party. “We Europeans really have to take our fate into our own hands.” That is just what President Trump has been telling the Europeans since the beginning of last year’s U.S. election campaign, demanding in particular that Europe pay more for its own defense. Both Trump and Merkel, moreover, say they want the euro to strengthen against the U.S. dollar. That...