I think Russia would go nuclear only as a last resort. They know American retaliatory strikes will be on the way within 90 seconds and they know how they are targeted. Putin’s name is on one of the first.
I think Putin is smart enough to not get drawn into something tit for tat with the US. I would bet he knows he’ll come out on the short end. Knowing that Russia is better prepared to survive an all out exchange, my bet is that he would surprise us by going big right off the bat, .
Then you add in the rumors of his failing health...
I don’t think, as long as the continental US isn’t hit, that we would respond with a launch on Russia.
If we launched against Russia, and they did the same, we are all done for. Neither side has the ability to intercept all. I think if the Russians used a tactical weapon, our bluff would be called. And we would fold, I think.