When it will happen

https://demonocracy.info/infographics/usa/us_debt/us_debt.html

One day USA wont be able to even pay interest for its debt. It grew from 1.5 trillion USD to 20 trillion USD since 2011.
So the end is nigh. Important is to get the right time when the paper money became useless and you will need gold pieces (or gun) to get food and staff...

graphics

The Federal Government's Interest Rate Problem

While little remarked upon or understood, the United States government has an interest rate-related problem of its own when it comes to the debt and the deficit.

That is, tax revenues are not sufficient for the federal government to make either principal or interest payments on the federal debt.

So each time a principal payment is due – the federal government issues a new debt to get the money to pay off the old debt.

And each time an interest payment is due, the federal government issues new debt to make that interest payment. Indeed, borrowing the money to make interest payments is the source of over half of the annual federal deficit.