On Saturday night, I turned on my phone after the Jewish Sabbath and discovered that a white supremacist had massacred 10 innocents in my state. Most of the victims were Black, and the gunman reportedly targeted Buffalo, New York, because of the city’s racial makeup. According to law enforcement, the killer left a 180-page manifesto laying out his deranged grievances. The document makes clear that its author was animated by the "Great Replacement" theory, which posits that a sinister Jewish conspiracy is scheming to import Black and brown people into Western countries to displace the white race.