The doctrone of MAD became obsolete in 1960s. And even then it was more a wishful thinking rather the actual strategy. If Russia strike first and if the Russian strike is precise (as it was demonstrated with Oreshnik strike) USA lost all their silos, all bombers and more than half of SSBNs. Few survived SSBNs won't be able to cause "unacceptable damage" to well-prepared Russia. Therefore, after Russian counter-force strike you either accept Russian peaceful proposals (and lost only Alaska and California) or retaliate, kill, may be one million of Russians, but then, after their counter-value strike you'll be forced into unconditional surrender or virtually total annihilation.