AP Photo

Earlier this month, as a secular, liberal political coalition swept the polls in Libya, some Western observers hailed a “break in the Islamist tide” of post-Arab Spring electoral outcomes. Following victories for Islamists in Tunisia, Morocco and Egypt, it seemed stunning to find a Western-educated political scientist, Mahmoud Jibril, suddenly at the helm in Tripoli. Other observers, by contrast, noted the exceptional circumstances of Jibril’s triumph: not only had he achieved fame and acclaim in Libya beforehand, during the country’s revolution, by leading the rebel government in Benghazi, he also enjoyed staunch backing from his native Warfalla tribe, one of the most powerful tribal confederations in the country. These factors have been used to suggest that...