For more than a decade, Suleiman Anwar Bengharsa has served as a Muslim cleric in Maryland, working as a prison chaplain and as an imam at mosques in Annapolis and outside Baltimore. He gave a two-week course in 2011 on Islamic teachings on marriage at the Islamic Society of Baltimore, where President Obama made a much-publicized visit this year. But in the last two years, Imam Bengharsa’s public pronouncements have taken a dark turn. On Facebook, he has openly endorsed the Islamic State, posted gruesome videos showing ISIS fighters beheading and burning alive their enemies and praised terrorist attacks overseas....