Just to make sure everyone is up on the facts. It's not like Social security went and 'spent their surpluses'. There are several steps involved here.

1) The SSA brings in more money in FICA taxes than they need to pay out in benefits.
2) The SSA takes that surplus and buys T-Bills, just like countless other investors. The SSA is require BY LAW to do this with any of their surpluses.
3) As of LBJ's administration, the US Government started counting the SSA surpluses as if it were regular government tax receipts to mask the size of the deficit.
4) The debt crisis threatened to affect the SSA only in the respect that the SSA might not have been paid the coupons (interest) and/or bond redemption (maturation) would have impacted the SSA's checkbook. Since the SSA has been running at a deficit the last couple of years, they now NEED those interest and other bond payments or else they can't pay ALL (only most) of the benefits they're on the hook for.

As I said in another thread - it depends on how you look at it. The SSA either has a big batch of the safest investments on the planet or a piles of risky IOUs.