Earlier quoted context omitted.
It is not a Ponzi scheme if it is not always and necessarily growing.
Most western countries can't even afford paying the interest of their debt. So as it is, it is kinda necessarily growing. But the ponzi scheme aspect is rather the fact that countries can only pay back debt with new borrowing. If investors stop rolling their debt, even the US would collapse within a few months.
If that were true, the countries would be in default. And yet they are not.