They certainly can without even firing a shot. First, they demand we pay our debt...
Yeah, China has considerable economic power over much of the world should they choose to exert it.
When we got into Iraq we had to scramble to find a supplier of armor grade steel because China decided it was a good time to do a little price gouging on us. (Switzerland cut off our supply of computer parts for guidance systems for missiles.)
And after we say no, we will just keep paying the interest like always?