One doesn't need nuclear weapons to screw an incapable and 20th century equipped Russian Army - not even to mention their non-existing military leadership qualifications.
There will be no "regional war" conducted by e.g. Germany, France, Britain and Sweden against Russia. But in case of Putin going nuts like Trump - a common NATO response, upon a NATO member being attacked - led militarily foremost by the above mentioned and naturally also involving US Forces.
The only scenario that I can imagine Putin using nukes - is an imminent Russian defeat in Ukraine - which isn't a NATO member, and therefore will not result into a NATO nuke response.