Walter Russell Mead is professor of foreign affairs and the humanities at Bard College and editor-at-large of The American Interest.

The long-brewing crisis in Syria has entered a critical phase and it is changing the rules of the Middle East.  If the people keep marching and the regime keeps shooting, the Obama administration could face its toughest Middle East choices yet.  Will Samantha Power bomb yet another country in the region, or will she try to sleep nights with the blood of thousands of Syrians on her hands?

The bloody-minded and repressive Syrian regime — after Saddam Hussein, the slave-trading Sudanese and the gay-murdering and woman-stoning Iranians, the worst bunch of thugs in a nasty neighborhood — has ripped off the mask.  An estimated 80 plus protesters were killed Friday; at least 6 more when relatives tried to bury Friday’s dead.  The violence can easily escalate.

The outside world, preoccupied by the dramatic events unfolding across northern Africa and in Yemen, had not paid much attention to Syria until the last 36 hours.  But now the scale of the protests and the brutal response have caught the world’s attention.  Britain, France and the US have all condemned the latest violence, with the White House using some of its sharpest language yet.

This crisis could have legs.  Although Syria is not an oil exporter, every moral and political argument that led to the intervention in Libya applies more strongly to Damascus.  And while the political, national interest rationale for regime change in Libya is a little sketchy, the case for regime change in Damascus is close to ironclad....