Tax revenues are up substantially - unfortunately, spending is also - thus the interest on the debt gobbles an ever-larger chunk of tax revenue, which means more borrowing, which means more interest. Pretty soon, tax revenues will barely cover the INTEREST payments.
$20T @ 2% = $400B. 2% is a below average rate.
Avg rate is 5%.
$20T @ 5% = $1T.
5% is an average rate. The rate could go higher in the next 10 years.