A long-discredited antisemitic conspiracy theory is resurging—amplified by social media—and contributing to a noticeable rise in anti-Jewish sentiment. What once lingered on the fringes of the internet now circulates widely on major platforms, repackaged to cast doubt on Israel’s legitimacy, erase Jewish history, and cloak old prejudices in the language of “science.”

Last week provided a clear example. In an interview with U.S. Ambassador to Israel Mike Huckabee, Tucker Carlsonpressed Israeli Jews to undergo genetic testing to prove their ancestry from the ancient Jewish populations of the region. In doing so, he echoed the so-called Khazar theory—the claim that the original Jewish population disappeared after the Roman destruction of the Second Temple in 70 CE, and that most modern European (Ashkenazi) Jews descend instead from a medieval Turkic group that converted to Judaism. Once promoted by David Duke, a former Ku Klux Klan leader, this narrative has been revived online in recent years. But the premise collapses under scrutiny: the genetic research Carlson invokes has already been conducted—and it overwhelmingly contradicts the Khazar claim.