Either having to balance a budget or a downward cycle where more and more interest is required for debt, leaving less and less for function of government.
It would also mean $33T in assets disappearing from the economy. That's a massive amount that would bankrupt tons of individuals/companies that lent the money. $2.8T of that amount is the social security trust fund which means we need to also instantly cut social security too. $7T of the debt is held by other countries who wouldn't be happy with us either.