If you borrow from your 401K, you're borrowing from yourself, and you eventually have to pay it back. It's money that you owe, to be paid with funds that can either be used to buy jelly beans or put back in your 401K.
If the government borrows from Social Security, it takes that money out of itself and spends it out in the economy. SS and the government has a smaller pile of cash, and the government owes itself. When the money is put back, it's with funds that could either be used to buy bullets or put back in SS.
If the government borrows from Social Security, it takes that money out of itself and spends it out in the economy. SS and the government has a smaller pile of cash, and the government owes itself. When the money is put back, it's with funds that could either be used to buy bullets or put back in SS.