As long as the US dollar keeps being the number one reserve currency,the US debt can keep growing without any issues.The Federal Reserve will keep printing money and buying US government bonds and other countries will keep buying US dollars for their foreign transactions and national currency reserves.
The real problem will occur,when the US dollars stops being a global reserve currency.I'm sure that Russia,China and many more countries will decide to stop using US dollars in their transactions at some point.
The question is what happens next?Hyperinflation in the USA or the US government going bankrupt?Or maybe both?
That won't go on forever if the value of dollar keeps going down. Debt does cause this, when you have so much debt that you keep on printing money and everyone has trillions of debt from you, then it will not make sense to keep getting more and more of it. This is why some nations may try to switch to euro instead of dollar, even yuan as well. That way they would know there is at least a chance that they could get paid, so why keep it in dollars?
I am not saying that this will happen tomorrow, but as long as USA keeps getting their money more and more worthless, some nations will definitely start looking at other currencies or at least there is a risk of that happening.
Let's assume you're right. Question - let's simulate the situation? Well, for example, your country, businessmen from your country, have decided that it's time to abandon the dollar and switch to -.... Oh, what are we going to switch to? First you need to find a really high-quality alternative. Euro? Well, so-so - internal tensions, a "trend" to leave the EU, debts, problems with the Russian Federation, ... The Euro does not fit!
ABOUT! China and its yuan! Well, why not an option - a powerful economy, hates, at least indicatively, the United States and the dollar, wants world domination. Next steps? Your country sells goods, services to China.. You get a bunch of yuan, you want to buy, for example, ore in Australia, and
Australia says - no, give us dollars, we don't accept yuan
You are rushing about, you need ore - South Africa also says "why do I need yuan? Where can I buy something for them, except for China ... No, let's pay in dollars" . As a result, you are sitting with a bunch of yuan, and you understand that now you either switch to monopoly imports from China, or throw these pieces of paper out of your head, and continue to trade on the world market for DOLLAR