Eminent historian Paul Johnson, whom we lost this past January at age 94, labeled anti-Semitism an “intellectual disease” distinct from other generalized forms of racism. “In my view as a historian,” he wrote in 2005, “it is so peculiar that it deserves to be placed in a quite different category.” Surveying thousands of years of human history, Johnson judged it a “historical law” that anti-Semitism self-destructively boomerangs against nations practicing it, consigning them to a fate of decline and failure.