Senior citizens are a very active political group. How long would the government have to be in default before social security payments are delayed.
The answer below are based on the assumption that the intergovernmental transfers ($4.8 trillion) that the government owes to itself (a large percentage of which is the Social Security trust fund) will actually be paid back to the Social Security Department. If the government defaults, the SS Department will be in the same boat as other creditors. If you don't accept this assumption, the Social Security department currently does not receive enough revenue to cover outlays.
The Social Security Department puts it at 2033
Social Security’s total expenditures have exceeded non-interest income of its combined trust funds since 2010, and the Trustees estimate that Social Security cost will exceed non-interest income throughout the 75-year projection period. [...] After 2020, Treasury will redeem trust fund asset reserves to the extent that program cost exceeds tax revenue and interest earnings until depletion of total trust fund reserves in 2033, the same year projected in last year’s Trustees Report.
The Congressional Budget Office puts it at 2035, with a range of uncertainty of 80% in their simulations (between 2029-2045)
CBO projects that under current law, the DI trust fund will be exhausted in fiscal year 2016 and the OASI trust fund will be exhausted in 2038.