Do a walk through of what you're implying there - you're suggesting the US is going to lump trillions of dollars worth of inflation losses onto the voting public to protect foreign investors. At a time when the public are extremely twitchy and sensitive to price rises.
There is a clear risk that the US will instead lump trillions of losses on foreign investors and attempt to protect the purchasing power of their voters. It isn't like they're fooling anyone either way - they borrowed a bunch and can't pay it back. They can pretend they paid it back but the markets are going to respond to the magnitude of the losses and not the excuses. The leadership may as well let the bulk of the damage fall on people who don't vote in US elections - there isn't any particular reason to do otherwise.
The US could choose to tank their own currency but it'd be more orderly and the incentives certainly could be aligned to formally default regardless.
The domestic bondholders would pay the inflation tax and are all wealthy enough to have savings, ie, they are also taxpayers. They're not getting out of this no matter what happens; they're going to lose out.
The question is really do the bondholders directly eat the losses (20% foreigners) or US consumers and their tax base eats them (potentially ~0% foreigners although inflation is so complicated in practice it is hard to tell). It'd be pretty easy to handle the situation by a standard default and probably better for the voting base. The risk of the politicians breaking that way is obviously present.
It is risk, it doesn't even have to be likely. It is just the question of "will the bondholder get all the money they're promised?" and the answer can obviously be no. The US can't afford to repay their bonds, purposefully triggering vast inflation would be quite damaging to the US political class and there is a chance they decide not to. It isn't a negligible chance.
There is a clear risk that the US will instead lump trillions of losses on foreign investors and attempt to protect the purchasing power of their voters. It isn't like they're fooling anyone either way - they borrowed a bunch and can't pay it back. They can pretend they paid it back but the markets are going to respond to the magnitude of the losses and not the excuses. The leadership may as well let the bulk of the damage fall on people who don't vote in US elections - there isn't any particular reason to do otherwise.
The US could choose to tank their own currency but it'd be more orderly and the incentives certainly could be aligned to formally default regardless.