In other words, print new fiat so that the interest can be paid on the old fiat. In other-other words, the system is built on debt, and the national debt can NEVER be paid back, as the fiat to do so does not currently exist.
This is all necessary on a fractional reserve bankstering system.
The solution? build a PM-backed replacement system waiting in the wings, then when ready, collapse the fiat-based system. When people are then at the precipice, they will willingly switch to the new system, and forgeddabout the "national debt".