The Crimea is essentially Russian. The western side of Ukraine wants and deserves its’ freedom and identity.
We don’t need to go to war over Crimea. Let it go.
As for Europe, it’s time for them to defend themselves - with our help, rather than sitting on the sidelines and letting us do ALL the work.
Having served in Germany during the Cold War, I saw plenty of Europe sitting on its collective asses while we did all the work.
If there are tons of Russians in the Crimea (a river) , let it do a Kaliningrad Oblast.
(Dam the Bosporus and pump out the Black Sea.)
To the extent that the Ruskies go after the islamists, so much the better for the world.