Correct me if I'm wrong here, but aren't we locked in a weird cycle where the US sells its debts to continue functioning, but then much of the system relies on the revenue generated from those debts being paid by the US.
If a sell off were to begin the price of bonds would plummet. The first countries to sell would be least impacted, but eventually the later countries are in bad shape. You can say sell at the "exact same time" but that's not really how financial markets work.
I suppose the US is still more reliant on these bonds, but I'd imagine a crashed dollar would have pretty large ramifications globally.
Of course of of this will happen anyway if the US decides to invade Greenland.
I can see where countries no longer invest in US bonds, but may be forced to hold onto these to not take a budgetary hit.