(Kay Nietfeld/picture-alliance/dpa/AP Images) German Chancellor Angela Merkel in Ukraine on November 1, 2018 T he most famous geopolitical cartoon the London weekly Punch ever published was called “Dropping the pilot,” showing a weary Otto von Bismarck coming down the gangplank of a ship called Germany in 1890 after 28 years as chancellor. Angela Merkel has done only 13 years as her nation’s leader, though see seems like an institution. Now she is stepping down as leader of her Christian Democratic Party. Her departure marks a turning point in German and European history. She stays on as chancellor until the end of her term in 2021, and there has been talk in Brussels and Berlin of her moving to be president of the European Commission—the executive bureaucracy of the European Union, or the European Council on which sit all the heads of Europe’s government, soon to be minus Britain. The German horse cannot be ridden by two masters, and once her successor is installed in December,...