Russia neighbors to the south might have reason to worry, but to the west? Not so much. The Ukraine brought this on themselves. All they had to do is promise not to join NATO. I wonder what we would think of Mexico or Canada forming a military alliance with communist China? With Chinese troops, tanks and missiles on our border?
The U.S would strong arm them diplomstically. If that didn’t work they would invade them. And of course blather on with all the nonsense about morality etc