The government in Libya is still struggling to rein in the fractious but powerful local militias that became targets after the killing of American Ambassador Christopher Stevens in Benghazi. While the armed groups have sometimes served as local police forces under Libya’s interim government, they have proven a dangerous nuisance as the United States attempts to hunt down those who killed Stevens and three other Americans. Tens of thousands of Libyans mounted protests last month to spur the government to crackdown on the militias—but militia leaders say breaking up the groups has only led to more local unrest.