Actually, the law mandates that the Social Security Administration "invest" any money it has, which it doesn't immediately need, in U.S. treasury bonds. (And those bonds earn interest for the two trust funds.) So it's not like the federal government inappropriately raided the trust funds (one for regular Soc. Sec. and the other for SSDI.) In that sense, it is true that the government did borrow the money, just as it borrows money from anyone who buys treasury bonds - like you or me or the banks in our neighborhoods or the Rockefeller family . . . or the Chinese. But that's what was supposed to happen.

So, while the money exited the trust fund, it was replaced by valuable securities, the U.S. treasury bonds, which earn interest for the fund. The fund owns these bonds, which investors all over the world agree are one of the safest investments you can have. (At least, that's been the consensus and still is.)

So very much money comes into the Social Security program that they haven't needed to cash in those bonds. They just pay checks out of the money they get every month in social security taxes. The money coming in from workers has been a lot more than the money going out to retirees and the disabled. (Because the economy has generally kept growing and the size of the working population has kept expanding.)

However, we expect that a time will come when the size of the pool of retirees will be large compared to the size of the working population paying in. Then they got to start cashing in those bonds. The federal government will, most certainly, pay the fund what is owed on those bonds. It will get the money from taxes, or from selling more bonds to other parties who want to buy them. OR it will simply sell bonds to the Federal Reserve, who will purchase the bonds with money it prints on the printing presses - which has been done before and is no big deal.

We don't have to worry about the Social Security trust fund getting back the money it loaned to the government. We do have to worry about the government having some tough financial decisions to make, when money that it would have for other stuff starts going to buy those trust fund bonds. At that point, the government has to either raise taxes, sell more bonds to other parties, or cut things like Medicare or military spending.

You could say that the money in the trust fund was borrowed to pay for those wars in the Mideast and for Medicare/Medicaid because there wasn't enough tax revenue to pay for that stuff - mainly because Pres. Reagan and Pres. Bush, jr. didn't believe in making people, especially rich people, pay taxes.

One last point: A lot of the money that rich people saved by not paying a lot of tax has been sitting around in private and corporate bank accounts doing nobody any good. That means that rich people literally have more money than they even know what the heck to do with. A President Bernie Sanders would tax that idle money and put it to good use.