Yup, US nuclear power really has the Chinese quaking in their boots.
China is indeed a singular case.
In this regard, I think the case of Iraq and the Desert Storm are relevant. The reality of U.S. hegemony over Iraq was proven to the world by force, even if Saddham continues to live in a fantasy world. When a country's behavior crosses some unspecified line, in terms of acceptability to the U.S., then the reality of the hegemony comes under test. The U.S. has diplomatic, propagandistic, and economic leverage which it can bring to bear in this regard. An new test of U.S. hegemony is now coming to the fore in the cases of Iran and Libya.