Second, its critical that treasury bonds are denominated in USD. The us gov controls the monetary policy and can choose to inflate away the debt over time. This is in contrast to EM debt where they get trapped with foreign denominated bonds. See also the tensions around EU debt, greece, etc.
Argentina is doing fine. The real constraint would be that defaulting on the debt would cause a credit crisis and bank collapses.
The powerful people holding the debt will seek to change the government to one that obeys them