One never knows with an individual as desperate and deluded as Putin, but even he knows that if he were to use a tactical nuke, there would be an immediate overwhelming response to utterly destroy his military, no matter where located. The west would not have to use nuclear weapons. If Russia did attack a NATO country with nukes, there would be a corresponding nuclear response that would far overwhelm anything Russia might employ. I do not believe that even the most militant Russians are that stupid.