China has no interest in funding terrorist attacks against the U.S. or anyone else. They want to be a Great Power, not a rogue state.
Aside from nukes, which would draw an obvious and unstoppable reprisal from the U.S., China does not have the military capability to meaningfully threaten the U.S. They don't have the aircraft, ships, subs, landing craft, etc. And again, I don't know why they would want that.
They do have the means to threaten their regional neighbors, though, and some of them are U.S. allies. That's the WWIII threat: that Chinese regional aggression sucks the U.S. into a military confrontation on China's turf.