A short and pessimistic answer is: Argentina.
A slightly longer optimistic answer is: withdrawal from global hegemony and return to 1790 and The Constitution.
Basically the US can only afford to have such a huge debt because the reserve currency status of the USD creates huge demand for USD debt instruments (Treasuries).
If substantial parts of the world economy stop using USD for trade then demand for US Treasuries will drop and the interest rates the US has to pay will rise.
Because the debt is so enormous the US will not be able to afford to pay if interest rates rise, even to normal 8-10% levels. Sovereign debt default is then inevitable.
A short and pessimistic answer is: Argentina.
A slightly longer optimistic answer is: withdrawal from global hegemony and return to 1790 and The Constitution.
Basically the US can only afford to have such a huge debt because the reserve currency status of the USD creates huge demand for USD debt instruments (Treasuries).
If substantial parts of the world economy stop using USD for trade then demand for US Treasuries will drop and the interest rates the US has to pay will rise.
Because the debt is so enormous the US will not be able to afford to pay if interest rates rise, even to normal 8-10% levels. Sovereign debt default is then inevitable.