The U.S. Capitol

International financial markets reacted to the shutdown of the American government with remarkable calm on Tuesday. But there was also growing fear that the political impasse set the stage for a far greater problem later this month if Washington hits its debt ceiling and begins defaulting on Treasury bonds.

"It would be doom — it would be a lot worse than 2009," when the financial crisis caused a sharp downturn in Europe and the United States, said Thibault Prebay, head of bond management at Quilvest Gestion, a French asset manager.