So what? It's not like China can call the debt. The worst they can do is dump it on the market, whereupon banks and money managers across the globe will devour

So what? It's not like China can call the debt. The worst they can do is dump it on the market, whereupon banks and money managers across the globe will devour it like money-flavored hotcakes. There will be a brief market burp, and some change in USD value and interest rates, but at great fiscal expense to China. Disclaimer: IANAT (am not a trader).