[jon_richards]

What's really weird is that if the USA started inflating their debt away, the value of their debt would drop and they'd need to start borrowing at a higher rate.

As long as the USA willing to increase the size of their debt, that doesn't happen.

For this to continue, people need to keep lending the USA money, so that the USA can pay off their old debts. People are willing to lend the USA money as long as they don't think the USA will start inflating their debt away.

There isn't really a limit to this. Loans to the USA are stable because people keep loaning to the USA because loans to the USA are stable. The size of the debt doesn't affect that equation.