all it has to do is call in the debt owed on US bonds it bought from America.
And all the US would have to do is copy the USSR, China, Cuba and many other countries when they found themselves in debt, rule the debt null and void and nationalize all Chinese holdings in the United States.
As for the Russians, we went head to head against them on a regular basis back when I rode submarines for a living and the USSR was a real threat. Even at their height, we beat them hands down. Now I merely scoff in their general direction. They aren't worth bothering with.