Before a hate-filled 18-year-old murdered 10 and wounded 3 African Americans in Buffalo on May 14, he penned a rambling screed about replacement theory. The most common version of this whiny idea, imported from the more hysterical fringes of the French far right, holds that Jewish capitalists are importing cheap immigrant labor to replace more highly-paid white workers. Notoriously, the Nazis who marched in Charlottesville, Virginia in 2017 against the removal of Confederate statues chanted “Jews will not replace us.” The shooter who killed 11 Jewish Americans at a Pittsburgh synagogue in 2018 also espoused the idea of the “great...