Let's conduct a thought experiment. Say your house has monthly expenses of $100 and a monthly income of $200. Every month you save $100. Years go by and that savings grows and grows and eventually you have quite a sum, say $1000. You decide that since your monthly income exceeds your monthly expenses that you can spend that money and replenish your savings later. In essence, you are borrowing from yourself. So you take that money saved and write a little note, "will pay back later" and then proceed to spend the money.
Here's the tough question: after spending the saved money, how much money do you have? If you answered $0, go to the head of the class. It's not complicated. If I spend all the money I have saved, I don't have any money. What about those pieces of paper that say "will pay back later". Well, those are pieces of paper, not money. And until you actually pay them back, you've got nothing.
Here's another way to think about it. Imagine we have the same household income of $200 and instead of spending only $100 and saving $100, we spend the whole $200 every month and write ourselves little notes, "will save $100 later". Every month we have no money saved, only little notes we wrote to ourselves. Eventually we have quite a lot of notes. But if you're really astute, you'll realize that we still have no money.
Folks, Social Security is broke today. We are currently taking in less income than we are paying out in benefits. And there is no "trust fund". All that's in there are little notes.
I am always amazed at the duplicity of politicians. How anyone can say with a straight face that there is a trust fund, and that social security is not broke is beyond reproach. The reality is that if your household, our government, spends every cent it takes in as income, it doesn't have any savings. That's common sense.