Not that many actually. Look at what the OMB said about Clinton's policies had they remained in place. If the people keep electing representatives that let the rich pay zero taxes and make laws that prolong and increase the costs of pandemics then we'll default on the loans when we cease being the United States of America.

Most of the national debt is due to Republican shell games. They want to decrease the size and effect of government, so they first enact high tax cuts favoring the wealthy. Then that produces substantial national debt. It also negatively affects the effectiveness o government programs an services. Then they say, "See, we told you that big government does not work, and they scream for great cuts in human service programs to produce the artificial debt that they produced. It is both amazing and disheartening that many people fall for that crap.