There is no balance of power here...that is if you still maintain that this is not a proxy US-Russia war.
Russia has (a) Tactical Nukes & the means of delivering them (b) Conventional Nukes & the means of delivering them
The Ukraine has neither
Of course if you admit (which I do) that this is a proxy US-Russia war, then there is a balance of power and as such neither side will likely use Nukes first
Q: If Russia uses tactical nukes against the Ukraine will the US likely respond in kind?
If the answer is yes, then this is more likely than not a proxy US-Russia war, IMO.
