Governments do not go "formally" bankrupt, they just lose the ability to pay obligations (default), and they lose their ability to make loans from other governments.
Then the currency crashes, and people go back to bartering or using other currency.
Look at the current state of Zimababwe - it takes trillions of their dollars to equal one US$.
If the US cannot pay it's obligations, then services will go away, social security, defense, health, welfare, etc.... Other nations holding the debt may attack to get their money back.

The states are already in bad shape and are now going to the US govt for help just to meet their budgets. What happens when the US cannot help the states? Budgets will get cut by default.
State services in California are about to go to IOUs for payment. Try to buy groceries or electricity with an IOU?

Seems like the states have been heading south ever since Ronnie's ever so popular fed to state block grant system went into play. I never really understood any of it.