Don't forget, the US is the lowest-taxed Western country, so they have lots of room (and lots of inherent wealth) to tax. Whether they have the political will to do this, or the political will to reduce Defence Spending is an open question. But it's not inevitable. Hell, they can always do what other countries have done and abrogate debt or pay it down pennies or quarters to the dollar. Would work once.

Or, the country can break up with each portion rearranging its financing and resources accordingly. There's a number of options, if people choose to think beyond the next social message post.