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

What was the USSR and how is that not equivalent? Im not calling names but they were a state under Russian control for 60+ years. The Soviet Union fell and they were unable to hold their union together. Now Putin is attempting to collect what he sees as rogue states. I think Ukraine should be free and sovereign. But do you honestly believe the US would not do the same thing to keep one of its most valuable states from leaving the union.