Reminder: the US is the only country that has ever used nuclear weapons in war. It is also the only country that has ever used nuclear weapons against civilian populations.

At the time, no one really cared.

Since then, there has been a lot of media about how nuclear war is bad that started once the US had enemies that could attack it in a nuclear war.

But if the US attacked a non-nuclear state with nuclear weapons? There would be a lot of condemnations. But for most of the world, there would be no real change in their policy towards the US. Most of the leaders of the world have already internalized that the US, as a dominant empire, will commit any war crimes it deems fit and that there is nothing the rest of the world is willing to do about it.
The other nuclear-armed states are certainly not willing to go to nuclear war with the US about an attack that wasn't on themselves.
Do I think that the US public would condemn Trump? Frankly, every Democrat who said that we had to vote for Biden and/or Harris once they had supported genocide has already failed this test. I'm certain that they could also rationalize nuclear devastation. They'd condemn it because Trump had done it but defend it because the empire had done it.
So we're in an evil society, populated by a majority of evil people and led by 100% evil leaders. Is such a society willing to reject a nuclear attack? Maybe. Maybe not.
PS: Do I think that the US military would refuse to follow orders no I do not.
All of that said, it's vastly more probable that the US would do Israeli-style conventional carpet bombing than that it would switch to nukes. At least right away.