If he used a tac it would mean a rapid escalation and instant and horrible reaction. There is no point in using a weapon designed to be used against a massed army against the Ukrainian resistance. If he used on on an urban area, it would be WWIII, no doubt in my mind.

Even if a nuclear war was magically limited to a tit-for-tat response, and civilization survived, Russia would not survive as a nation, the rest of the world wouldn't allow it. Russia would be defeated and occupied, like Germany was, until they got their minds right, which would take decades if not centuries. Most importantly for Putin is that he would not personally survive such a stupid move.

https://www.democraticunderground.com/?com=view_post&forum=1002&pid=16453145

I shared an article discussing this possibility, in the context, I believe, of airing it out "in advance" to help prevent it from happening. My post adds info on "pre-bunking" as contrasted with de-bunking.

PS: I trust that President Biden has the best intelligence, advice and judgment. I won't second guess.

Russia Really Could Use A Nuclear Weapon In The Ukraine Conflict - The DEFCON Warning System

https://defconwarningsystem.com/2022/03/07/russia-really-could-use-a-nuclear-weapon-in-the-ukraine-conflict/

snippet:

This brings us to the dangerous option Russia has. A way to possibly end the war quickly.

A nuclear attack, a demonstration bomb over the sea or over Ukraine.
From Russia’s point of view, they could see such an event propelling Ukraine to surrender. Additionally, Russia may think that NATO, fearing what Russia is capable of, would refrain from responding. After all, it wasn’t NATO that was attacked, and any response would certainly invite Russia to counterattack on their home soil.
Would Russia risk it? It’s unthinkable. But is it impossible?

The DEFCON Warning System believes that this is an option that is on the table. Russia has many options. This is one of them. Doesn’t mean they’ll do it. In fact, let’s go so far as to say they won’t do it. But it is something that is considered.