If Obama/the U.S.:
-hadn't needlessly/uselessly sacrificed missile defense in Eastern Europe;
-let the Syria "red line" evaporate;
-been feckless and vacillating on virtually every foreign policy issue since 2009;
the situation might not exist at all. Our foreign policy has enabled these messes by projecting weakness and ambivalence, and ignoring tactics short of "boots on the ground".
What can should Obama do or say now? Not a lot. What could he have done or said previously? Different question...
I will, based on the above, amend my earlier post to say that regardless of what other Presidents or politicians may or may not have done / would do in a similar situation, no President in my memory, going back to Carter, has looked as weak as Obama. Even if they only blustered, they at least blustered about real consequences. When Obama blusters, he blusters about, "If you're not careful, we'll start a Twitter campaign!".
This entire administration seems to think the world is a Utopian university campus, where protest will illicit change, or at least concession, if only to shut the protesting students up and stop them from blocking the door to the campus tofu take-out.
I also wonder if this situation in Ukraine would exist to the degree it does now with an administration that
didn't call Mitt Romney crazy for suggesting that the Russian Federation was a potential geopolitical threat to US interests.