原因是babyboomers 要拿的退休金超过现在员工交的SS税和利息收入。 SS盈余是不能用来做它用的。当然你放在银行的钱银行也拿去做投资了， SS的钱政府也借去它用。SS手里拿的是联邦债卷。
The Social Security actuaries project that Social Security benefit payments will begin to exceed payroll tax revenues in 2012. Total trust fund income — which includes interest earnings that the trust funds receive on the Treasury bonds they hold, as well as income from payroll taxes — will continue to exceed benefit payments until 2019. In 2019, the combination of payroll tax revenues and interest earnings will no longer be sufficient to cover all benefit costs, and the trust funds have to begin redeeming the bonds they hold to raise the additional funds needed. The actuaries project that the trust funds will cash in these bonds fully in 2029. At that point, the Social Security surplus now building up will be exhausted.(7)
