At present, Russia, like many other Nuclear Powers, has a second strike only policy. This means that in the event of war with another nuclear power, Russia would only launch it's Nukes if it detected a launch from the belligerent side. They would never be the first to use nukes. The United States is one of the few nations that did not adopt a second strike only policy, opting for one that basically said we will keep the war restricted to conventional arms until we detect Nukes inbound OR we think a tactile nuclear strike is in our interest (Read: We're about to lose and the only way to win the battle is if all the opposing conventional forces were suddenly vaporized). Considering which of the two is the only nation to ever use nuclear arms in actual combat... and you could see why the Russians were so nervous about the West... which was politically opposed to Soviet style government.
It also explains why the Soviets added a "dead man switch" to their nuclear command and control. They will launch if a signal is not received from Moscow within a certain amount of time (the engineering of this system is such that the only way for Moscow to fail to send the signal is if Moscow suddenly was no longer on the face of the earth. Russia has historically been very vulnerable to decapitation strikes. Their capital is much more important than any other city. It's also one of the reasons Russia is pretty difficult to invade.).
That all said, many Nuclear War scenarios, especially in the 80s when the cold war started to go towards a hot one, was that NATO-Warsaw Pact war would start off with a flashpoint crisis of some sort (Trouble in East Berlin or a Crisis in the Middle East) which raise tensions with both powers until the opening salvos of a conventional war begin, at which point, it's a conventional war with infintry, tanks, air battles, and naval battles. The thought is that NATO would have the naval advantage, Warsaw would have the land advantage, and it would be a dead even split on air superiority.
At some point, one of the land battles is going bad for their side... they can barely hold the line and enemy reserves are enroute to the front lines and once there, they will break through. For whatever reason, losing this position in the opening actions of war is unacceptable so the side that is on the ropes will launch a tactical nuke at the re-enforcements because its all they have left. The side that is nuked sees this on early warning detections and, with the fog of war, have no way of knowing if it was the only nuke.
But the thing about Nuclear arms is that the best national defense against a nuclear bomb... is to have a nuclear bomb of your own. That, and the ability to convince the enemy that if backed into a corner... we will use it.
It's estimated that in a total nuclear war between the U.S. and U.S.S.R. that all but 3% of either side's Nuclear Arsenal will be delivered to the intended target when launched. And that both sides had 30 minutes of travel from ground launch points until they reached their target. Now, to the side that sees that lone nuke fired at their re-enforcements... they have no way of knowing if that missile is a shot that will win the battle, or the first shot in a war ending salvo. They have no way to talk to the other side at this point. They have less than 30 minutes at best to retaliate before they lose that capability and the lives of everyone on the home front. It doesn't matter if it's one launch or one thousand launches... if they want even a hope of a chance to win this war, be it for mom and apple pie, or perogies and suka, there's now only one thing to do. Launch everything, and hope that the 3% of arsenal that survives is your own. Of course... the only way to learn their true intentions, is to see if they launch all of theirs before you've launched all of yours... either way... who lost the war is now decided... all that can be said is that we will know who won sooner... because at either rate, nobody does.
And what is troubling, is that in so many scenarios, the implication if not outright statement was that it was the U.S. losing ground that pressed the button first... and those were the predictions from the West... because as was said in the film "War Games," in global-thermonuclear war, the only winning move is to not to play the game. It's how we won the Cold War.
Much like in my family when my sister suggest we play Monopoly (sorry, after writing all that sobering stuff, I had to get a laugh in somehow.).