In reply to aircooled :
Im not actually concerned with the damage of nuclear artillery, although I am concerned about the health issues associated with them for the people of Ukraine. I am worried about the USs position to respond to it.
If nuclear artillery use by Russia leads to a bolstering of support for Ukraine (which I think is most likely) and the US wants to maintain we are only supporting someone at war with Russia, not actually at war ourselves position, which has its obvious benefits, they cant do much except wag their finger at Russia and maybe send the next thing we initially told Ukraine no on. Last I checked it was F16s. I see this as more escalation, and will just cause a response from Russia, which will require another response from the west. Its also unlikely to soften Russia's position, even more ammo for the "we are actually at war with the west" state propaganda.
The other thing the US can do in response, and I do not think its actually likely , but is to give up the facade of not being at war with Russia. This could look a bunch of different ways but is obviously pretty bad for us and everyone.
I think its less likely, but possible, the usage of nuclear artillery can lead to less support in the US. If it gets used it will get covered by media stateside, largely to make Russia look even more evil. Sure some people will respond with we must stop Putin, but I think a bunch of people who have been told all the talk of nuclear escalation in the war was over blown and unlikely and all the people talking about it are scaremongers, then all the sudden all the news outlets keep saying nuclear and talking about "nuclear attacks." We already have support trending down, and all of the sudden maybe this war is as dangerous as we where warned. If support by the public drops quickly, the politicians will continue to do what they want, for a short time, but we are about to gear up for election season, and for a short period of time politicians will be worried about doing something Americans dont want. Obviously without the USs support Ukraine is in a much worse position.
What Im saying is all of the responses by the US are a E36 M3 sandwich. Our choices are escalation, massive escalation, or Ukraine not being able to defend themselves.
Truthfully the best response, for Americans (Im aware its all terribly bad for Ukrainians), would be no response and wait out the news cycle, but as Frenchy said that wont happen.