world to see. Obama will embark on his second term with the global economy at a crossroads. In the US, the uneven and weak recovery has been sustained by extraordinarily expansive monetary policies and ongoing large fiscal deficits. While corporate coffers hold mountains of cash, private investment stagnates. In Japan, solid economic performance remains elusive, while prime ministers succeed each other at a breathtaking pace. Likewise, Europe is on life support, thanks to European Central Bank President Mario Draghi's astute maneuvering and promises of unlimited intervention in sovereign-debt markets. But unemployment is at its highest in decades and growth has essentially stalled, even in Germany, while the troubled southern economies are mired in deep recession. The situation in Greece, moreover, has become socially unsustainable; Greece is small, but a total collapse there could have very negative financial and psychological effects elsewhere. The world's emerging-market economies are in better shape; but, while their underlying trend growth in potential output is much higher than that of the advanced economies, there is no cyclical de-coupling. The world economy is an interdependent whole: trouble in any important part of it is transmitted globally. That is true beyond the purview of narrowly macroeconomic problems as well: for example, the need to address climate change can no longer be ignored. The US cannot determine the world economy's future on its own, but the course taken by America nonetheless has huge global importance, given that it remains the largest economy and retains considerable influence in venues such