They hold Billions in IOU’s so to speak to go to the treasury with when they need money.
SS is not the real problem funding wise, it is Health Care Costs that are killing us.
We take in about $450 Billion on Medicare taxes, but we spend $2.5 Trillion on spending. That cannot continue. A good part of that is for Medicaid. The government pays 85% of Medicaid and states 15%.
So what happens to Medicaid if the Feds can no longer pay, the states cannot pay it. So realistically you might see all Medicaid spending at the state level slashed 85%. This is one of the reasons we are closing in on $40 Trillion in Debt.
IOW like any other US govt bond it is considered a cash equivalent.
The problem is 90% of your healthcare costs are going to be last nine months of care. Feel free to start there and extrapolate.