President Obama committed America to the cause of the Libyan rebels based on the theory of R2P -- a responsibility to protect innocents, the innocents of Benghazi and other rebel strongholds, who presumably faced slaughter at the hands of loyalist forces of Col. Gaddafi.  This is the dreamy theory of diplomacy pushed by Obama advisor Samantha Power.

But now that the rebels appear to be surging, if they take Tripoli, will they slaughter the enemy tribesman who supported dictator Gaddafi? If that threat were imminent, wouldn't the United States have an obligation to switch sides under the R2P doctrine?

Adam Garfinkle considers the possibilities  on The American Interest:

There are reasons for thinking that the likelihood of the slaughter in Benghazi was far lower than the likelihood of a slaughter coming soon in Tripoli. Gaddafi may have thought back then that just the threat of mass violence could dissipate the rebellion, or weaken it fatally. Arabic is very good for threat making, and Arabs over the years have become masters at using language as votive acts. (There is a long tradition, just by the way, of leaders hiring poets to curse their enemies. There is as a result a whole genre of Arabic literature of this sort. And to those familiar with the Hebrew Bible, it will occur that this is not just an Arab hobby, but one practiced widely in the ancient Near East as well, as the used-to-be-very-well-known story of Balak and Bilaam attests.) Westerners eavesdropping on this internal conversation frequently take what is being said much too literally.

The Obama administration, in other words, naively interpreted overblown rhetoric, and now fails to comprehend the tribal dynamics:

NATO is not in a position on the ground to do anything about it. NATO, fighting without the United States, has not been in a position to do very much about anything, which raises a point I will follow up just below. Clearly, the rebels who might be soon advancing on Tripoli do not recognize a clear distinction between civilians and combatants. Tribal rules say that all adult males are fair game. Given the widely available military technology of our time, however, and the Libyans' lack of training in using that technology surgically, it is very unlikely that women and children will remain safe regardless of traditional prohibitions against harming them.

There are no good options for Obama now. I guess that smart diplomacy is working out about as well as hope and change. Garfinkle concludes:

 All I know is that when a government engages in military activity on the basis of a nonsensical premise, there is a price to be paid always down the road. We are now pretty much down the road.