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...