About half of the debt is to... the US government. And all of it is in US dollars, that the US government can print.
So the US could get out of debt tomorrow if they wanted, forgiving the loans it made to itself, and then printing enough to pay off the rest. Which presumably wouldn't impact its ability to lend money to itself.
The tough part for me to wrap my head around is why the debt is important at all, given the US is more or less fully in control of it.