Leaders of the G20 nations, which account for 90 percent of the world economy, are set to meet in Cannes, France, this week. The summit comes at a tumultuous time for the world economy, as the European debt crisis rages on and China debates its possible role in any bailout. Challenges to global economic recovery are broader than just those facing Europe though, as President Obama wrote late last week. American action to fix problems at home, chief among them high unemployment and weak demand, is needed to spur a global response and global growth that will, in turn, lift the U.S. economy. Leadership also means looking beyond today's emergency: In order to create balanced, sustainable and equitable growth, the G20 - and Washington - must quit "careening from crisis to crisis."