The perpetrator of the Pittsburgh massacre was a denizen of far-right Internet communities, spurred to action, it seems, by news of the approaching caravan of would-be immigrants from Honduras. This combined with his belief in a Jewish plot to undermine the U.S. through mass migration—a plot in which the current president functions as a mere pawn. Meanwhile, a week after the shooting, police arrested a New Yorker named James Polite for writing “Die Jewish Rats” on the wall of a synagogue; they also suspect him of attempting to burn down seven schools and yeshivas in Brooklyn. Yet, although Polite’s attitude toward Jews closely resemble those of the Pittsburgh shooter, his political orientation is the opposite. Liel Leibovitz writes:

Polite, twenty-six, is not a white supremacist. He is African-American, was raised in part by Jewish foster parents, and was sent to Brandeis University with the help of a charity run by the New York Times. He was a Democratic-party activist, a protégé of the former city-council speaker Christine Quinn, and a one-time City Hall intern who, according to the Times, worked on “initiatives to combat hate crime, sexual assault, and domestic violence.” . . .

If the left is honest, it will spend the coming days and weeks asking how someone educated at a fine liberal university, on a scholarship from a fine liberal newspaper, could graduate from a job with a fine liberal politician—helping curb hate crimes, no less—to trying to intimidate and incinerate Jews. It’s a question worth lingering on. Polite wasn’t a disgruntled loner with a loose social network and no systems of support. Throughout his troubled life, he received one opportunity after another to rise above his hard beginnings. . . .

Those of us not beholden to blinding partisan commitments are saddened but not surprised. Anti-Semitism is so pernicious precisely because it eats through ideological convictions, afflicting left and right alike. And no matter what you think of the president’s comportment, cases like Polite’s make it impossible to deny that the left has just as much of a Jew-hatred problem on its hands, if not a much bigger one: if the second-most-powerful progressive politician in the city with the largest Jewish population in America couldn’t detect, let alone curb, the arsonist on her staff, the problem is much graver than many might care to admit. Before more troubled maniacs attempt more violence, it’s time for real soul-searching to begin.

Two extraordinary events demonstrate something important about Israel’s most fervent adversaries. One was a speech given at something called The People’s Forum (funded generously by Goldman Sachs), which stated, “When the state of Israel is finally destroyed and erased from history, that will be the single most important blow we can give to destroying capitalism and imperialism.”

The suggestion that this tiny state is the linchpin of a global, centuries-old phenomenon like capitalism goes well beyond anything resembling rational criticism. Even if Israel were guilty of genocide, apartheid, and oppression—which of course it is not—it would not follow that its destruction would help end capitalism or imperialism.

The other was an anti-Israel protest that took place in front of New York City’s Memorial Sloan Kettering Cancer Center, deemed “complicit” in Israel’s evils. At organizers’ urging, participants shouted their slogans at kids in the cancer ward, who were watching from the windows. Given Hamas’s indifference toward the lives of Gazan children, such callousness toward non-Palestinian children from Hamas’s Western allies shouldn’t be surprising. The protest—like the abovementioned speech—deliberately conveyed the message that Israel is the ultimate evil and its destruction the ultimate good, cancer patients be damned.

The fact that Israel’s adversaries are almost comically perverse does not mean that they can be dismissed. If its allies fail to understand the obsessive and irrational hatred that it faces, they cannot effectively help it defend itself.