Even in a country that has suffered devastating terrorist attacks in the past five years, the macabre beheading of a schoolteacher Oct. 16 has stunned France, as politicians and regular citizens grapple with religious extremism in their midst—igniting a political battle that could threaten the prospects of President Emmanuel Macron. Samuel Paty, a middle-school history and civics teacher, was on his way home from work Friday afternoon in a quiet suburban town north-west of Paris when an attacker cornered him on the street, and stabbed him repeatedly, before decapitating him.