re: How is this different than a state leaving the US.

You should read up on the history of that region. Those two nations have been rivals since the Middle Ages. A thousand or so years ago, Kyiv was the seat of the empire. There’s a much larger timeline here, long before the Soviet Union.

So no, Ukraine was not a state of Russia and this comparison doesn’t hold water.

And BTW, I hate this for Ukraine and am pulling for them…but still want the US to stay out of it, at least in an official/direct capacity.