International buyers will cool on the idea of holding US debt.

US policy will artificially lower the interest rate to stimulate the economy. Also, the spending of the federal government will continue to increase above the tax receipts.

This will result in inflation. Which is great if you owe money, since you are paying it back with cheaper money.

But, the interest rates being low will make it easier to borrow? The resulting divide by zero in the economy (meaning an exception that there is no solution to) will result in the US government repudiating it's prior debt and making the 'new dollar'.

This will cause a couple of years of chaos.