The Muslim Brotherhood, among the most powerful forces in Egypt, is facing perhaps the worst crisis in its 80-year history. Its members have been gunned down in the streets. Its new headquarters have been ransacked and burned, its political leader, President Mohamed Morsi, abandoned, threatened and isolated by old foes and recent allies. It is a steep fall for the pre-eminent Islamist movement in the region, and especially surprising for a group that was elected just one year ago. Its critics say the Brotherhood remains stuck in old divisions, pitting Islamists against the military, and has failed to heed the...