Europe’s Greek tragedy has now entered its final act, with potentially fateful consequences for the global economy—and for Barack Obama, whose reelection may hinge on the decisions of Germany in the coming weeks. The 2012 election will pivot on the public’s evaluation of the president’s economic stewardship, and a perceptible decline in the U.S. growth rate—which a badly handled Greek exit from the Eurozone would cause—could easily spell the difference between victory and defeat. Obama’s fate, then, may well lie in Angela Merkel’s hands. That doesn’t mean, though, that there’s nothing he can do about it. What are the economic...