First: that debt will be repaid. The people who own those T-bonds will redeem them and get their money. This is an important distinction; you buy T-bonds becaus

First: that debt will be repaid. The people who own those T-bonds will redeem them and get their money. This is an important distinction; you buy T-bonds because you know they’ll be paid back. The total value of the debt is an almost meaningless number. As long as people keep buying US debt, we’ll have the money to pay the debt off. (Strictly the US could just print the money it needs to pay the debt right now - the question is whether the resulting inflation would be worth it). The rest cost of the debt is interest payments. As long as those stay at a manageable fraction of GDP the US is just fine. If GDP increase 10% but debt servicing only increases 5% then the servicing payments are effectively 4.5% smaller. In the next decade our problem is less likely to be total quantity of debt than increasing interest rates (which are very low right now).