Those federal IOUs are rightly accounted for in federal finances not as assets but as part of the Gross Federal Debt, subject to the nationaldebtlimit.
August was a particularly unfortunate month: it began with a reckless stand-off over raising the nationaldebtlimit and a downgrade to America's credit rating, and ended with a hurricane.
The Obama Administration has floated the possibility of pushing legislation that give the President power to increase the nationaldebtlimit without having to go back each time for Congressional approval.