Right now the US fulfills the three essential conditions for monetary sovereignty: 1) it issues its own non-convertible currency, 2) which it allows to float on international currency markets; and 3) it owes no debts in any currency other than dollars. Because it is monetarily sovereign, and can always meet its obligations the US can never be forced into insolvency.
It can become insolvent due to Congressional decisions such as failing to raise or repeal the debt ceiling, or Executive decisions such as failing to use its platinum coin minting authority to fill the public purse and then pay its bills once it has reached the debt ceiling. But again, it cannot be forced into insolvency by external financial or economic factors that are beyond the control of the Federal Government (including the Congress).
