The reaction to the events of October 7 has made the growing radicalization of the progressive wing of the Democratic Party—and, in particular, its indulgence of anti-Semitism—more clear than ever. And it has highlighted President Joe Biden’s role in resisting the leftward pull of those progressives, a stand of increasing importance not just for his party, but for the country as a whole. In the early-morning hours of a Jewish holiday, Simchat Torah, the terrorist group Hamas launched an unprovoked attack, committing the worst massacre of Jews since the Holocaust. Civilians were intentionally targeted, and constituted the overwhelming majority of casualties. Israeli families were burned alive while hiding in their homes. People were decapitated. The bodies of babies were riddled with bullets. U.S. Secretary of State Antony Blinken, speaking at a Senate hearing, told of a boy, 6, and a girl, 8, and their parents around the breakfast table. The father’s eye was gouged out in front of his kids. The mother’s breast was cut off, the girl’s foot amputated, and the boy’s fingers cut …