There is a serious possibility that the US will have to face this question if not now, sometime in the not too distant future.
First, "risk" does not mean certainty.
Second, what is meant by "nuclear war?" Full scale Armageddon? Or limited use of tactical weapons?
I don't think it's worth destroying all complex life on Earth to stop Putin, but I seriously doubt that it will come to that.
I do think that we should never give in to a crooked little thug.
I voted yes because oppressive totalitarian governments always become more oppressive even after they achieve their objectives. Their success only emboldens them. In our current situation, if we allow Putin to rebuild the Russian Empire, he will be in a better position to challenge the US. Remember, Alaska was part of Russia at one time. And it is not just a question of governance or or national borders. Putin is an evil leader. And evil leaders are almost never replaced by anything other than evil leaders.
Better us than some small country that has nothing to lose. If we allow the conquer of sovereign nations, how long until one of them defends themselves with a nuke? If I was a small country about to be conquered and I had the ability to nuke my aggressors in a bid to try to save myself, why should I just roll over?