This is an extremely complicated question. But basically there is a LOT of power that comes from being the most powerful country on the planet. Even more comes from being the highest producing GDP country on the planet. (Although we are not the highest per citizen) Countries and individuals around the world view US Debt as VERY safe, because if we go down as the most powerful and richest country on the planet...Then we have entered a very, very dark place. As a result of this US debt(bonds) are an extremely attractive investment in a volatile market. The amount of debt the US has doesn't really matter because of how powerful we are. There is a lot of truth to what Luke says in how powerful capitalism is, despite at times how brutal it is. It's what has made us so powerful. Other countries don't have the luxury we do... IE. Greece. Countries and people around the world don't really want to invest in debt in Greece, because who knows how they will rebound...
The federal government offers three categories of fixed income securities to consumers and investors to fund its operations: Treasury bonds, Treasury notes, and Treasury bills. Bills are the shortest duration, notes 2nd and bonds are usually 20-30 years+
Each security has a different rate at which it matures, and each pays interest in a different way.
One thing they all have in common, though, is their reputation of being based on the full faith and credit of the United States government. Investors can expect a high degree of safety and a steady, but unspectacular profit from each of these securities. Upon maturity, these bonds, notes, and bills return their face value.
Here is a brief overview that talks about it in more detail. There is some concern into how things are now vs how they were a few decades ago... The debt is increasing substantially year over year. Corporate taxes as a percentage of tax revenue is a huge sticking point for me as the trickle down theory just does not work. If you keep giving the rich more and more money they will spend it on themselves, not on others who actually make them the money.
https://www.investopedia.com/updates/usa-national-debt/