Is the U.S. Headed toward Bankruptcy?

U.S. Comptroller General David Walker told 60 Minutes that he is afraid Medicare with the prescription drug benefit is leading the country to bankruptcy. Here's a quote:

Walker shows Kroft long-term projections from the Government Accountability Office that assume the status quo continues, with the same levels of taxation, spending and economic growth. By the year 2040, Walker says, "If nothing changes, the federal government is not going to be able to do much more than pay interest on the mounting debt and some entitlement benefits. It won't have money left for anything else . . ."