It isn't only about the Ukraine. How much of the old Soviet Union are you willing to cede back to Putin in order to buy his help in securing peace in the Middle East? Kazakhstan? (Putin has already said it's not a “real” country.) The Baltics? Putin wants to put Humpty Dumpty back together again, and won't be satisfied until he does.
The biggest mistake in the US regime-changing policy is ousting forceful rulers who protected their minorities and didn't let the Muslim crazies do their jihad thing. Still haven't learned the lesson in Syria.
My point is I'm willing to cede Putin anything where he'll stop ISIS from spreading. And Europe should be, too. The EU has a horrific problem with Jihadists doing Europe. I just don't get why they wouldn't want Putin there to protect the eastern flank.