I would suppose that depends on what NATO's response is. They could swiftly disable Russia's conventional forces in Ukraine and the Black Sea without creating an existential threat to Moscow, which is what I expect it would take to provoke nuclear warfare.
Putin is rational and realizes he cannot stand against NATO and hope to survive
Putin is not rational
In case of 1, we should make it clear there is no path to victory for him. In the case of 2, it doesn't matter, he's going to go crazy already, the die has already been cast.
Fucking bring it. As an SSBN submariner in the US strategic nuclear navy, please give me a reason to flip that switch. Not a soul in the strategic forces would even hesitate to respond to a valid and authentic EAM.