Russia is firebombing Ukraine.

[DFW]

22. Even if they do, they wouldn't make use of it

The Ukrainians aren't out to obliterate or colonize Moscow or the Russians. Their objectives aren't a mirror image of Putin's.

Putin wants his Ukrainian SSR back in the neo-Soviet fold. The Ukrainians want to stay out of it.
Putin is basically indicating that if he can't have his way, there will be no Ukraine left.
The Ukrainians are saying, please just go home, and leave us alone.
That sounds like "irreconcilable differences" to me, and Putin will not go home unless forced to. His celebrated Red Army may have great balalaika players, singers and dancers, but have proven themselves less than formidable in actual combat. This is not something a major world power can afford to have be known worldwide. He shows himself to be a failure if he uses nuclear weapons on a neighboring country that has none, themselves, and never attacked Russia of their own accord.