Disease is reversible—rot isn’t. Representatives Ilhan Omar and Rashida Tlaib brought the disease of anti-Semitism into the upper echelons of the Democratic Party when they were elected in November. The party could have fought the disease. It chose instead to nurture it. And that’s when the irreversible rot set in.

The rot explains why Democrats, from Speaker of the House Nancy Pelosi on down, are vigorously defending Tlaib’s recent lies about Arabs welcoming Jews after the Holocaust. It doesn’t matter what Tlaib or Omar say, how blunt their Jew-hatred is, or how often it’s aired. A defense pact is already in place that covers all calumnies against the Jews. Both the Democratic leadership and the liberal media establishment will back these bigots against any and all charges of anti-Semitism in return for smooth relations with the social-justice left. It’s a monstrous deal made by people too weak to defend their party and speak the truth.

During a Yahoo podcast over the weekend, Tlaib said that she gets a “calming feeling” when she thinks about the Holocaust because “it was my ancestors, Palestinians, who lost their land and some lost their lives, their livelihood, their human dignity . . . in the name of trying to create a safe haven for Jews, post-Holocaust, post-tragedy. . . And, I love the fact that it was my ancestors that provided that, right?”

Wrong. At the time, Haj Amin al-Husseini, the grand mufti of Jerusalem, was a supporter and ally of Hitler. When the two met, al-Husseini told Hitler that they shared the same enemies: “the English, the Jews, and the Communists.” The two went on to scheme about how best to set upon and destroy the Jews of the Middle East. What’s more, the Arabs regularly massacred Jews in Mandatory Palestine.

Lies are the lifeblood of anti-Semitism, and there’s a purpose to Tlaib’s false history. It serves to bolster the lie that the Jews waged war on a friendly and welcoming people, stole their land, and condemned them to ruin. Anti-Semitism depends on lies because its very motive is to hide the truth of one’s own failings and lay blame on the Jews. The history of anti-Semitism is, in a sense, a history of wicked fabrications: From Jewish deicide, to the blood libel, to the claims of Jewish sorcery, to The Protocols of the Elders of Zion, to the idea that Jews were tipped off about 9/11, to the claim that Jews push the U.S. into wars, to the outrage over Jews supposedly buying politicians, to lies about Israel’s founding.

Tlaib and Omar are exemplars of this tradition, peddlers of anti-Semitic folktales. In addition to spouting revisionist history, Tlaib has accused America’s Israel-supporters of dual loyalty. Omar has done that and more, claiming that Israel has hypnotized the world into not seeing the evil it perpetrates, and stating that America’s pro-Israel policies are simply purchased by those who support the Jewish state.

They’re also Democratic congresswomen with the full support of their party. “Policing my words, twisting & turning them to ignite vile attacks on me will not work,” Tlaib tweeted recently. “All of you who are trying to silence me will fail miserably.” She’s right. You can’t reverse rot. It goes in one direction and doesn’t stop until it has destroyed its host.