> Any state that fires an offensive nuke is toast

Do you really think the U.S. would attack Russia? Do you think the U.S. would allow the EU to level Russia (which it probably doesn’t have the ability to do)?

I don't think that the US would attack Russia as retaliation for a nuclear strike against Ukraine. But the US would probably step up aid to Ukraine. And more importantly, nuclear escalation would likely trigger economic sanctions by key neutral trading partners such as India.