I don't claim that we would have a automatic nuclear response.
What I would expect is:
1) We would not respond with nuclear weapons.
2) We would go to an immediate response mode.
3) Russia would be immediately shut down economically and we cease relationships with countries supporting Russia. Totally isolate them. That includes countries like India and Turkey who walk both sides of the line.
4) The gloves would be off in supporting Ukraine. We would fully arm Ukraine.
But the nuclear fallout would also reach Russia and other Eastern European countries, varying on what type of nuke. These tactical nukes are similar in size to Little Boy but only 2% of fissile material in Hiroshima Bomb actually detonated.
So, the miltary claim can be made that the impact is acceptable but people are not going to view this escalation of nuclear weapons as acceptable. After all the liberals set the doomsday clock at its highest level ever. Imagine how the people will react to the use of the word nuclear weapons.