It’s a story all too familiar from European history, from 12th-century England to 20th-century Russia: a non-Jewish child goes missing or is found dead, and what is in fact a tragic accident is blamed on the Jews. Mob violence ensues. A week ago, this familiar pattern repeated itself when an eight-year-old Arab boy went missing in Jerusalem. The next day he was found dead, apparently having drowned in a pond. But by that time, rumors had spread—with help from Congresswoman Rashida Tlaib—that Jews had kidnapped and murdered him. Aaron Kliegman writes:

Acting on this unsubstantiated claim, Palestinians searching for the boy marched toward a nearby Jewish neighborhood, believing its residents had kidnapped him. Demonstrators threw rocks at police, who blocked the mob from entering the neighborhood. Ultimately, twelve people were injured and three protesters arrested.

The rumors of kidnap and murder spread on social media. A Twitter account named “Real Seif Bitar” tweeted that Abu Ramila was “kidnapped and executed” by a “herd of violent Israeli settlers,” who assaulted him and threw his body in a well. The Palestinian politician Hanan Ashrawi retweeted these allegations. . . . And then, Rashida Tlaib retweeted Ashrawi, sharing the vicious lies with her nearly one million followers.

Once authorities concluded the boy had likely slipped and drowned, . . . Tlaib deleted her retweet. But she never apologized, and despite her self-serving acknowledgement a few days later, her followers may still think Jews murdered Abu Ramila.

Whether it’s Israelis supposedly wantonly murdering Palestinian children or medieval Jews drinking the blood of Christian children—the effect of these libels is the same: poisoning public opinion against the Jewish people and stoking the oldest hatred. And while Tlaib may believe she is speaking truth to power when she makes false claims about Israel and Jews, responsible people in her party must hold her accountable for spreading misinformation and propping up illegitimate claims without scrutiny.

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.