America has gone through withdrawal phases before, usually after a great war: World War I, World War II, Korea, and Vietnam. Some were longish, like the retreat between 1919 and the late 1930s. Some were brief, as after 1945, 1954, and 1975 (when the Vietnam War ended). In each case, war-weariness translated into "Come home, America", as George McGovern famously proclaimed during the 1972 presidential campaign. In each case, the rebound eventually followed because the world wouldn't quite accommodate itself to America's reflexes. Fresh and old threats demanded American attention because others proved unable to fashion and secure a new balance of power.
Though America's longest wars, Afghanistan and Iraq do not add up to "great wars" like World Wars I and II. The entanglements in the Greater Middle East were very expensive, and with little to show. No wonder the nation wants to go home. Since 1919, though, history whispers that the "concert of nations" will degenerate into a cacophony of trumpets and kettledrums unless America wields the baton. Yet conductors keep the orchestra in line only when they read from a compelling score and stay onstage 24/7. Barack Obama, alas, is a reluctant and distracted maestro. Deep in his heart, one fears, he would rather be like Greta Garbo: "I want to be alone."