Completely agree on the Western conventional response. That should be the response at least. One of my biggest fears is that Putin calculates the West lacks the will to mount the major conventional response you describe and thinks the psychological impact of a tactical nuke would scare everyone into ceasefire.

Also, I’m not as confident as you that an insider would assassinate him. Maybe if he went for total nuclear annihilation, but I can’t see it with a tactical nuke, especially if it has Putin’s intended effects as described.