As the Russian said, it would come down to tactical nukes and I think Putin would use them on troops. Next problem, Europe doesn’t care and doesn’t want to fight except for former USSR states that are also threatened. The biggest problem is logistics. Russia’s border to our half way around the world. Being realistic and supporting Pooty Poot are two very different things.
We are, and always have been ready to fight with tactical nukes and their equivalent, I don’t know why you suddenly think that going nuclear is only possible for Russia.
NATO is ready to fight and includes most of the former USSR states, and most of NATO is in Europe, it is why we preposition our gear there and maintain tens of thousands of men, getting ready to meet Russia is nothing new to NATO.
NATO would be fighting from home, Russia would be trying to invade and having to deal with logistics.