If nuclear weapons are used it is doomsday. There are no qualifiers. The idea of getting away with a "tactical" nuke is fantasy. Our response would be total and immediate. There's no time to hesitate or wait for the effects.

If "tactical" nukes are a thing why hasn't anyone used them since 1945? Seems like they could have been handy in Syria or Afghanistan. There's no shortage of examples of nuclear powers going to war with non-nuclear non-NATO countries in the last 77 years. None of them involved nukes in any capacity.