How would the West respond if Russia uses a nuclear weapon in Ukraine?

[Yoda]

We have to use nukes on Russia then, as awful as that would be. Can't really think of another scenario. If we don't use them after one Russian nuke, the threat is gone.

This is my line of thinking as well. Putin is a terrorist with nuclear weapons. What's the only thing worse than that? A terrorist with nukes who knows the West will not respond with nukes if he uses them first. Putin would literally be able to hold the world hostage if we were to show indecision in such a scenario.

[Yoda]

https://www.theatlantic.com/ideas/archive/2022/06/russia-ukraine-nuclear-weapon-us-response/661315/

This article is a good read into various ideas floating around the powers that be (schlosser also wrote a really good book on the history of nuclear weaponry). The general consensus seems to be that if russia was to launch a tactical nuke on a military target, the US would respond in conventional means, through for example targeting the russian navy - as well as using the moral high ground to get the fence sitting nations away from Moscow. Especially interesting bit about the Obama era training exercise on how to deal with a russian invasion of the baltics (Obama's top guys recommended a nuclear attack on Belarus, Biden's allies recommend purely conventional response).

You know what, I'm in the proportional response camp as I believe not doing so would be inviting Putin to view us as unwilling to use nukes in any scenario (which obviously would be a disaster that results in him becoming a completely unleashed nuclear-armed terrorist), but if Russia launched a tactical nuke I could see, for example, us taking out the Russian fleet in the Black Sea as a proportional response. That would be acceptable.