They just need to pay it back in cybercurrency. Get some saps into thinking that
GovCoin has worth. (Made up GovCoin as a governments idea of a cybercurrency scheme ). Those who buy into it with real money pay
off down the debt.
Edited that to "pay down" vs "pay off" as for I doubt it could ever be corrected without a collapse and reset. Even if they stopped spending now which they cant do because they spend more money then they take in from tax payers, it might only delay collapse and then a monetary reform for a reset like all other countries out there that have had their money system collapse and then the old money is obsolete and they start over. The biggest problem though is that the USA has a lot of countries and people riding on its economic shoulders and so it wont be a simple money reset of a 3rd world country, it would be really bad and likely war would break out as there is need for food and fuel etc and the money is worthless, and in the shadow of the failed fiat currency I have doubts that precious metals would even save people from starvation as for you cant eat precious metals and so food and fuel would obtain a worth greater than what some heavy shiny metal that while rare there are tons of these precious metals around the world and food and fuel itself is more valuable than that.
At one point I thought about how much money made could be absorbed by numismatists. When less money is circulating it potentially has more worth. So get some saps to collect coins that are mass produced and offset inflation by the collectors involuntarily absorbing some of the inflation potential. Just think if all the state quarters, presidential dollars, and the rarely seen 2009 pennies, SBA dollars, Eisenhower Dollars, and all other clad mass produced change 1965 and newer in the USA all of a sudden was used to buy goods as for money in savings and in hiding doesnt really have a value to topple the economy. Its all fiat money and too much of it too quickly to buy goods is a bad thing.
Additionally economic collapse could come from people spending too much. As for if too much money went to buy goods vs sitting in bank accounts and in stocks it would flood the economy with paper that otherwise when its tucked away its not a problem, but when too much of it shows up too quickly it causes inflation as there is to much to go around and the printing presses print massive amounts of money in hopes that people will stock pile it to offset the fiat pyramid which is tied to national debt.
