Eighty years ago, my uncle Irwin Gerson celebrated his bar mitzvah in the Bronx. It was March 27, 1943, and World War II was raging. In his speech—which his granddaughter recently discovered in his files while working on an oral-history project with him—he admitted that he felt odd rejoicing “against a background of blood and tears, a ruined world.” He emphasized that “the enemy has undertaken the total annihilation . . . of our people.” Irwin’s words belie the claim that Americans didn’t know about the Nazi war against the Jews. On Tuesday, when the memorial siren wails for Yom...