Constant attacks by ethnic Russian "separatists" (i.e., Russian-backed nationals inside Ukraine) have been steadily cutting away pieces of Eastern Ukraine since Crimea was seized.

Today, it appears that they have blown a Malaysian commercial airliner out of the sky, killing all 295 people aboard. From 33,000 feet, with a sophisticated missile that clearly came from Russia, and recorded communications between Russian separatists and their Russian intelligence advisors.

With a number of foreign nationals killed aboard the plane, including (unconfirmed yet) up to 23 Americans aboard, Obama might have to actually respond. But so far, Obama has just responded with vague impotent "the world is watching" rhetoric.