Your post assumes that Ukraine is worth engaging in a nuclear war over.
It isn’t for the United States. For Ukranians, if they had nukes, I have no doubt they would use them against Russia. But is isn’t us. And it isn’t worth it. They aren’t worth it. They are not our allies or friends, and have never been unless they need something.
It isn’t “capitulation” if you have no business being involved in a fight.
There is no possibility of a nuclear war over Ukraine
Do not take counsel of your fears...... General George Patton