Going from 50% deficit spending to paying off equivalent of 100% of GDP (which enjoys a 2-5% annual growth) amounts to "won't be able to". We'd have to cut spending by 1/3rd just to stop increasing the debt. We'd have to route all federal revenue to debt for 5 years to pay it off. Ain't happening.

Ah, but most of the US debt is denominated in US currency... It's a convenient loophole to use if it ever becomes a more serious problem.

Yes, if tanking your own currency, probably bringing down the economy and starting a panic, counts as convenient.

Problem there is: there's only $4T in actual currency, but $18T in federal debt.

It's not like we'd have to print more gold.