M.A.D. no longer really applies to urban Russia, they've been fortifying and prepping for a nuclear attack since the cold war. Putin has said they could keep the 3 largest cities in Russia completely intact after a nuclear attack, with enough underground bunker space for the entire city of Moscow to run for 20 years underground. Supposedly, Putin claims the entire population of Moscow has been prepped.
Putin has been preparing for a nuclear showdown and has publicly commented on it in interviews last year. He said something to the effect of "Moscow has bunkers, and food and water for everyone in the city, does New York City? Washington?" He added, I hope we can resolve this peaceably, speaking about the U.S. in Syria, where we are already in a proxy war with Russia, but any attack against Russian forces (in Syria) would result in dire consequences for the U.S. There would be many casualties in a nuclear attack to be sure on both sides, but something tells me Russia is better prepared than the U.S.
It only makes sense that there would be another "Cuban missile crisis" of our time or similar events, especially given Trumps bold take on things. Russia has been developing the Bomba, or super Nuke, that is about 100 times larger than the Hiroshima bomb. The U.S. air to air missile system (which intercepts missiles) could likely get about 75% of nukes launched at us. That means if Russia sent up 100, 25 would get through. Not exactly an iron dome, unless we have better tech and they're not saying?