[USA-FRANCE]

They can’t use tactical nukes. It would be World War III if they did.
A “tactical nuke” is a misleading diminutive... In reality it has about the same explosive power as the Hiroshima nuclear bomb.
If one of these bombs are used, the fallout would also contaminate Russia itself and large parts of Europe. Thus triggering NATO response.

[Who is John Galt?]

They can’t use tactical nukes. It would be World War III if they did.
A “tactical nuke” is a misleading diminutive... In reality it has about the same explosive power as the Hiroshima nuclear bomb. If one of these bombs are used, the fallout would also contaminate Russia itself and large parts of Europe. Thus triggering NATO response.

"Triggering NATO response?" Ukraine is not a member of NATO. No NATO State with nuclear weapons would risk annihilation over the use of tactical nukes in Ukraine, unless the person in charge was absolutely demented... oh, wait...

[Sunsong]

I agree.

if putin/russia uses any kind of nuke, all bets are off

russian would likely be destroyed

I am sure that putin/russia has already been told that

[rdcbn1]

Just restating Russia's emerging military doctrine. They claim they have developed a new generation of micro nukes to complement their inventory of strategic nuclear weapons. They feel that the micro nukes are small enough to be sub threshold for a large scale strategic response given the Russians ability to mount a massive large scale nuclear response. They feel that they can use them to win in theater level conflicts. They may be right. As a practical matter, it really does matter how anyone else feels about the merits of their strategy- it only depends on whether or not they believe they can get away with it and their willingness to use them.

[PLMerite]

“In reality it has about the same explosive power as the Hiroshima nuclear bomb.”

The yield of the Hiroshima bomb was about 15KT. Much smaller-yield weapons now exist. I’ve read estimates as low as ~100 tons.

But it is the “nuclear” part that is the actual threshold.