As far as I can see the Chinese have nothing to gain by ruining you. If they
did decide to cash their chips, the US would be ruined, but the Chinese would lose a gigantic market, which is one of the main things driving their current economic boom. Plus they have nothing to fear from your military apparatus, because economically you're so dependant on them as they are on you.
I also found
this illuminating. Hard facts work much better than gut feelins.