MAD only works if you are convinced there will be a serious response to the initial strike. You are convinced that there would be a massive response regardless of where the strike takes place - I am not, based on the US not being attacked itself.
And I dont see how you can say why would Russia do this or that for fear of annihilation, without asking the same questions of NATO.
To be fair, none of this is going to happen anyway, as we can see the Ukrainians are completely running out of steam now, they cant even get men to fight any more.
Ukraine has a soldier shortage. Though many have volunteered, others are dodging the draft.
www.bbc.co.uk