Russia isn't going to cross NATO lines. Even if they do, NATO can defeat the Russians without nuclear weapons. I can't believe I have to say it but escalating to a nuclear war is a horrible idea.
There's still the hope that nobody, not even an imperialist Putin, would be willing to risk the total destruction of his own country if not of human civilization over some territorial ambitions.
Luckily, this is Russia. There is always someone willing to stab the tzsar in the back when the time comes.
So the solution of the OP is to be madder than him and start nuclear war first?
I wish there were someone to replace the mad tzar, its long overdue