That "interest" was never booked and paid by the Treasury. It was credited to the Trust Fund. Every single year. WILL be booked and paid NOW by issuing NEW debt to cover the old interest. When Social Security was running a surplus, it didn't "need" the earned interest to pay benefits. So the interest "bought" more bonds, making the balance of the fund larger. This was no different than if the fund had bought bonds in the open market and re-invested interest and principal payments into new bonds. Now that the fund is paying out more than it collects, yes, the Treasury has to sell new bonds to give the Trust Fund the money needed to pay benefits. The FACT IS -- that interest was never paid during the life of the debt. Like it is on REAL bonds. It was paid and bought more bonds. Just like real bonds re-investing the interest.