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

[Statilius the Epicurean]

I imagine it would respond with a conventional NATO air campaign designed to destroy the Russian military in Ukraine and disable any further deployment of tactical nuclear weapons. NATO has dominance in a conventional conflict so a nuclear response would be unnecessary.

If despite a conventional NATO intervention Russia continued to use tactical nuclear weapons effectively or say escalated to NATO territory, then I think you may see a nuclear response in kind.