And when Putin threatens nuclear first strike unless the west removes sanctions, or abandons the baltic republics, what next?

At some point you have to just call their bluff. Earlier is better than later. Putin himself knows that he'll be the first casualty in nuclear war, and I doubt very much that Putin's deputies would go along with a plan that results in the annihilation of the Russian people. He's playing a high-stakes game of chicken.

What does 'call his bluff' translate to in this context? Not take the threat of a nuclear war seriously and engage with Russia militarily anyways as-if the threat didn't exist?

Yes. Use NATO air power to tip the scales in Ukraine. They seem to be doing pretty well by themselves, even just a little help may be enough.

Putin is gambling that the west is too cowardly to fight, and so far he's right. Hitler made the same gamble in 1936.

> Hitler didn't have nukes and super-sonic missiles

While relatively late in the war so it didn't have too much strategic impact, the Nazis literally invented the supersonic missile.

I meant to say 'hypersonic' nuclear icmbs