Its a world economy now plenty of buyers. Our leaders should be ashamed of trusting commies.
Of course, it would hurt us too by increasing inflation and real interest rates, which if bad enough, could drive us into a recession. But I don't see any reason to think it would hurt us any worse than it would hurt China.
Hence I don't think this is a credible threat. They're just blustering.
Still, I do think we're borrowing way too much. We've got to get our deficit spending under control, and individuals need to save more. Relying on foreigners to finance our massive consumption binge is just plain not healthy.