For all of my adult life, the Le Pen family has felt like a shadow hanging over my head. Jean-Marie, the father, used to make jokes about the Holocaust. He was a former French paratrooper in Algeria who was accused of torturing prisoners. Then along came his daughter, Marine, who looked less threatening but more ambitious. Then her niece, Marion, who proved even more reactionary. The Le Pen influence appeared to be growing, but I always had the naive idea that “reasonable” people, from the right as well as from the left, would never let them win. It proved true...