Like most American Jews I know, I spent Oct. 7 scrolling through social media, listlessly pushing my toddler on a playground swing as I swiped between images of burning kibbutzim, fixing dinner to television images of a modern-day pogrom. Yet for all the horror of that day, I was not especially surprised that a group founded in 1987 to destroy Israel by killing Jews was doing just that. Hamas was, in comedian Chris Rock’s famous formulation, the tiger that “went tiger.”  It was the response of American progressives that left me by turns outraged and perplexed. As a group, we American Jews had proven ourselves to be reliable liberals who have voted Democratic for decades. We had marched with Martin Luther King Jr. and fought to preserve Roe v. Wade. Some of the closest advisers to Presidents Bill Clinton, Barack Obama, and Joe Biden were, or are, Jews. None of that mattered anymore. Suddenly, our shade of blue was no longer palatable to factions of the liberal establishment. Oct. 7 marked the final phase of a rupture that had been widening for years. No longer is the Left’s hostility to Jews a fringe preoccupation. Since the Hamas attacks, large swaths of American elite culture have treated Jews like a transplanted organ the body suddenly refuses to accept. If history is a teacher — and history rarely misses an opportunity to teach the present a thing or...