Last May, as he claimed the Democratic nomination, Barack Obama was ahead among Jewish voters 2 to 1. Yet, according to cable-and-blog wisdom, that was a serious problem for him. Jews—you know, “the demographic”—had voted 3 or more to 1 for Clinton, Gore, and Kerry. Jews are only about 2 percent of the population, but they make up almost 4 percent of actual voters. There are, famously, almost half a million Jewish voters in southern Florida alone. If, say, 100,000 defected to McCain, Obama would likely lose the state, even if the chads don’t hang this time. Jews are…