We have fleets of nuclear armed submarines constantly at sea just for the purpose of making Russia (or anyone) pay for a surprise strike.
Like, say, two SSBNs in Atlantic, twenty missiles each. If they bear 3 warheads each, it makes 60 warheads in one SSBNs salvo. Moscow's ABD can easily intercept 100 incoming warheads. 120 incoming warheads, of course, will be gambling, but for the total destruction of Moscow one needs roughly 50 100kt warheards (like typical W76-1 warheads). If the Russians attack first, and their attack is well planned, it means, that they already have half of Moscow's population evacuted and another half - sheltered. It makes that the losses will be counted in tens, may be hundreds of thousands, but will be pretty acceptable.
If the Russians, as a jesture of goodwill, after their first counter-force strike (with minimal collateral damage), suggest "humanitarian pause" without attacks against cities (to evacuate civilians) and thinking about rather generous Russian peace terms (the USA are returning Russia Alaska and California, but still survive as an independent state), there are pretty good chances that the USA won't retaliate at all.
Retaliation strike may cause significant, or even terrible losses, but will they be acceptable or unacceptable (in the current circumstances) depends on the possible alternatives.
Even France has a substantial nuclear submarine fleet that is large enough to collapse Russian or American society if they unleashed it
The launch of a singe SSBN won't cause neither Russian, nor American society. Vice versa, it may cause consolidation of the survivals under the flag.
No one could possibly win a nuclear war, which is why it will never happen
It depends on the definition of victory, but any war can be won. The question is that some strategies can be risky, and some strategies may be very expensive in the terms of human lifes. And in some situations Russia (or America) can decide that further appeasement is more dangerous than a nuclear war. And if the nuclear war is inevitable - then a first counter force strike is definitely safer than the second one (which, likely, might become suicidal).