Earlier quoted context omitted.
Why would China want to bankrupt the U.S.? They're a massively export-dependent economy and the U.S. is one of their biggest customers.
Sure, but there is more happening than just that. If China decides it wants to pursue its territorial claims against Japan say, then the mere threat of dumping T-bills will give the US pause before intervening. China only really needs the US while it is bootstrapping itself into a developed economy - once it has huge internal markets, it won't need them.
Interest rates would likely rise from their current close-to-historic-lows, but that's nothing that would scare the U.S. from defending one of its closest and most important strategic allies.
I'm really curious how you get from "China owns 8% of U.S. government debt" to "The U.S. would have to pause before defending Japan against Chinese territorial aggression."
Japan, by the way, owns 7% of U.S. debt.