You are badly misinformed. For the SS surplus, the U.S. government "buys" special obligation bonds, not Treasurys. These bonds are not tradeable on any market

You are badly misinformed. For the SS surplus, the U.S. government "buys" special obligation bonds, not Treasurys. These bonds are not tradeable on any market and do not represent an actual financial asset, the way a Treasury bond does. They are literally pieces of paper in a cabinet in West Virginia. They are truly IOUs on a sticky pad. There are no assets behind them, and there isn't even a legal obligation for the government to repay them or anyone "contributing" to SS. (see http://en.wikipedia.org/wiki/Flemming_v._Nestor http://en.wikipedia.org/wiki/Flemming_v._Nestor) The interest payments in the budget are actual repayments to Treasury bond holders, but NOT interest payments on SS obligation bonds. The government makes the SS interest "payments" with additional IOUs to the trust fund, NOT actual tax dollars. This SS interest is an accounting tool only, and is not part of federal budget outlays.