Yes, but Putin is not Hitler, we're not in the 1930s and Russia is not Nazi Germany. His support in Russia is rather half-hearted and the morale of his army is not good. There's nothing to indicate that Putin is able to mobilize his people in the way the Germans were driven to a nationalistic frenzy in the '30s. There is no chance that Putin will even consider another invasion, short of sending troops to Transistria to formally annex it. The whole point of this botched "operation" turned into war seems to have been to quickly decapitate Ukraine. The blitzkrieg against a poorly equipped country, with limited air capabilities and dated ground forces failed. Attacking a NATO country, which can muster the full force of the alliance would be suicidal. Even if he attempts it, which I doubt he will, it will be disastrous for him. Having said all that I doubt that option #2 would provoke a nuclear strike, although I'm not sure how effective it would be in ending the war. Unless of course the Russians are soundly defeated in Donbas, at which point Putin might be tempted to use a tactical nuke as a last-ditch attempt to get what he wants.