Atomic, Biological, Chemical
The US has huge arsenals of all of these weapons, a shortage of conventional ammunition would be the perfect excuse to use them to defend the “rules based international order”.
Dispite the later 2 being illegal for a country to even posess and the first legal for a contry to posess but illegal to use… so one has to wonder, what rules are there in this “rules based order”?
Fingers crossed though, if and when they do launch- the rest of the world must return in kind and 1000x over. The rest of humanity is not defenseless, and if they wish to use such WMDs the US best prepare for MAD and to be eradicated off the face of the planet, this is the deterrence game the US has forced the rest of the world to play and if they want to push their luck they will die by it.