Nukes are all Putin has to threaten with, just like Bully N. Korea.
Its rather one of many options. That is the reason we don`t see it happening already.
In reality, they both know better than to do such a stupid thing.
Why stupid? You think world biggest magnates would harry to commit suicide in a global nuclear holocausts? No, they won`t. For a few countries and cities obliterated, they won`t.
In fact, Russia and Putin can even do favor to somebody on the west of Europe or in the States. You think magnates of USA are all 100% united? You think Protestant magnates don`t have old frauds with Catholic magnates within States and in west of Europe?
Think again. Behind open wars are wars in the shadows.
And if it were to happen, you and I would never even see the flash or hear the boom so who cares.
I believe that in this moment, neither Poland, neither Serbia, neither the USA populace can fear imminent nuclear blast. In case that things escalate, if after first Russian warning nuking of few targets, somebody in USA make serious mistake, then it goes globally.