The federal government has been borrowing Social Security's surpluses for decades and issuing the program IOUs in return. However, the ability to pay those IOUs depends on the Treasury borrowing more money on global bond market at affordable rates. That's hardly a sure thing.
For years, policymakers have reassured the public that Social Security will be solvent for decades. But federal spending and income data from the Treasury reveals that Social Security is already deep in the red, with outlays exceeding payroll tax revenues by $76 billion in 2010 alone.