Whilst I sort of agree with you, ANY nuclear strike by Russia on any NATP country (should) be followed by a massive nuclear strike and make Russia uninhabitable for the majority of the population.
I can see 2 big problems.
1 Putin is quite old and may come to the conclusion that he will die soon anyway, so why not take the nuclear option and many millions more people with him?
2 The other problem is that with Trump taking over in the USA, nobody has any idea (probably Trump also) what the US response will be.
The US will probably try to remain neutral, until the US forces are attacked directly on the ground, at sea or on the US mainland.
That will be a major problem for Trump. Whether to aid his allies or his enemies.
It may also cause a problem in the Middle East between Israel and all the Arab states around them, which may also go nuclear.