While economic challenge will dominate the summit, the agenda runs deeper.

In talks on the sidelines, Obama will confront the bloodshed in Syria and the nuclear threat in Iran. He will meet with Vladimir Putin, who has returned to the presidency of Russia. Their talks will be scrutinized, given tense U.S.-Russian political relations and deep divisions over Syria.

Obama was to head to Mexico on Sunday night after a weekend with his family in their hometown of Chicago. The summit runs Monday and Tuesday.

Europe's entangled financial crisis, from debt woes in Greece to banking trouble in Spain and high unemployment all around, has become the single biggest threat to the U.S. economic recovery. The signs of worry are clear at the White House and in the words of Obama, who can draw a straight line from the fate of Europe's economic strength to his chances of a second term.

Obama is prodding European leaders to give world markets some confidence, and fast.