this article "the national debt graph by president" that explains how the debt got where it is

[1939]

5. Well, professor

Large surges in the current deficit normally occur when tax receipts go down. Tax receipt variation is normally caused by two things, strength of the economy in terms of employment and capital gains.

Look at a graph of income of the top 1% over time or of income inequality over time. Both spike in times of great capital gains and both crater in times of capital losses.

If we had three or four years of virulent inflation like 25% a year, the national debt would be trivialized as compared to GDP because the national debt would then be denominated in cheaper dollars.