I agree with your last point . Would depend on what sort of nuke was used as to how the US responded but (several) of those things on Kandys list would likely happen . A full on war is unthinkable for anyone and unwinnable for either I believe .
A single low yield tactical could be something putin would consider but even then there'd be a huge reaction from the US,I believe non nuclear reaction , and I doubt putin would be able to get a net gain out of it as Kandy has pointed out , russia has vulnerabilities outside russia that have not yet been threatened .
The best value putin has with his nukes is likely the threat of them . Costs nothing .
The only option is to do whatever is required to avoid nuclear conflict.
