When Erik von Kuehnelt-Leddihn wrote his 1974 book Leftism: From de Sade and Marx to Hitler and Marcuse, he dedicated it to “the Noble Memory of Armand Tuffin, Marquis de la Rouërie.” Tuffin was a French aristocrat born in 1751, and one of the first Europeans to come to the aid of the American colonies—even...