This whole thread has been both disturbing and fascinating at the same time, with some much better informed posters than I am. For what it's worth, I don't think a deployment of Russian tactical nukes would result in a nuclear response from NATO. I think NATO would more likely carry out a direct attack using conventional forces, perhaps destroy the Black Sea Fleet for example, there is the capability to do this as I understand it. Also Russias tactical nukes would be deployed using cruise missiles which can be taken out with Ukraines existing air defenses, to be honest though I can't see what advantage Russia would get from using them, what would they attack? Tactical nukes are for taking out enemy concentrations like a carrier group or tank column, Ukraine keep their forces widely distributed only comming together when attacked or to mount a counter offensive.