"meaning the Treasury/budget will have to make up the difference."
By redeeming the bonds that were issued previously. It is only in 2042 or 2052 depending on whom you ask, that they run out of bonds to redeem too. At that point, under current projections, benefits would decline slightly for some period of time.
The bonds were only IOU's, tough to redeem.
Basically the government will have to add to the deficit to fund social security in 2018. Or, raise the retirement age, increase FICA taxes, lower benefits.
OR, Fix it.
Besides the fact that SS is a pay as you go system and the bonds from the SSTF must be redeemed using real money, the benefits will decline approximately 25% in 2042 if all the bonds are paid off. By that time, our economy would be a disaster with over 70% of the federal budget being consumed by entitlement programs and another 25% servicing the debt. Doesn't leave much else for discretionary items like national defense. LOL