The Arab Spring heralded a profound shift in the Middle East, bringing to power Islamist movements which had previously been operating in the shadows. The Muslim Brotherhood stormed to victory in Egypt and emerged as a key player in Libya’s nascent political arena. Meanwhile, An-Nahda found itself catapulted into power as the head of Tunisia’s coalition government. For a while, it looked as though the region was entering the dawn of a new Islamist age.But navigating their respective countries through difficult and painful transitions ultimately proved too challenging for these forces, and, just as suddenly, the Brotherhood was dramatically overthrown in Egypt and left severely weakened in Libya. In Tunisia, An-Nahda managed to pull itself through...