From what I know the U.S. Treasury owns money to several agencies of their own and that is including your own Department of Labor which I think handles the 401(k) accounts. The government itself cannot borrow your benefits, pension, and other plans for you when a financial crisis happens since those benefits are solely allocated to you, they can only borrow the allocated budget the agency have or if they have any excess or unused budget left lying around. Not unless there is a law where it clearly states that the US government has the power to legally steal your own retirement benefits when times like this happen there is no way I see that the government will be taking your money.