It's not really such a novel idea. During the Cold War the Soviets did seriously consider creating a tsunami by exploding a massive nuclear device, similar to Tsar Bomba, at the bottom of the ocean floor. Some people, like Sakharov, supported it as a way of deterrence: plant the bomb and inform the U.S. it can be detonated at will.
All of this is interesting and what not, but Russia can already send America back to the stone age and has been able to for generations. We can do the same. Even China can, and some Western European countries too. The only difference here is the method and creativity involved.
And even if they nuked Yellowstone and even if that did trigger some 2012-style cataclysmic eruption, we'd still have a ton of 2nd-strike options that would allow us to retaliate and turn all regions of Russia with civilization into ash.
Wouldn't detonating a couple of warheads at a very high altitude do the trick by creating a massive EMP, essentially knocking civilian power grid out (which would inevitably cause the utter collapse of economic and social fabric)? Of course since crucial military installations necessary to launch a counterstrike are protected against the EMP. Even if you somehow managed to destroy or disable land based nuclear forces, you still have the subs out.
So yes, the basic concept of a Mutual Assured Destruction remains the same.