Eurointelligence founder Wolfgang Münchau has a thoughtful article on what Putin may or may not do. 

Please consider What are the Odds?, emphasis mine.

I have received a number of emails over the last few days from correspondents who assert that the risk of a nuclear war was small, or that it was unlikely. It is worth reflecting on the meaning of these predictions in detail. What does unlikely mean when we are talking about a nuclear war?

I can translate it for you. It means: "I have no clue. But I have a feeling." That feeling is based on assumptions that may sound plausible, but that we cannot be sure of. We think we know what Vladimir Putin considers to be in his strategic interest. We think some brave soul in the Russian command structure would heroically refuse to comply with a presidential nuclear launch order. We may think that these weapons are as dysfunctional as Russia's tanks, that they explode at launch or mid-air. Or we think that there might be a coup against him before he has the opportunity to pull the trigger. 

We can assert the probability of an earthquake, and attach a number to it. But there is no way we can do this here. We have no data and no probability distribution, and the usual weasel words are not helping us either.