You are joking...If the Ukraine Nuked Russia with a US Nuke, it would be WW3 & MAD (Mutually assured destruction )
IMO MAD was the reason for the Cold War otherwise the US would have Nuked Russia in the 50s/60s.
There has been a balance of Nuke powers since the 50s and now with China teaming up with Russia , that balance will likely be maintained well into the foreseeable future, IMO.
So the best that the US can hope for is proxy conventional wars whether that be against Russia, China or both to wear them down economically so that they can't afford to maintain the arms race.
