SAN FRANCISCO — Tech billionaire Elon Musk faced backlash from some Jewish leaders and at least one advertiser Thursday after he again embraced an antisemitic conspiracy theory, the latest in a pattern of his echoing anti-Jewish bigotry going back years. 

Musk sparked the criticism with six words he posted Wednesday afternoon on X, the social media app he purchased a year ago. Responding to another user who had accused Jews of hating white people and who had expressed indifference to antisemitism, Musk wrote: “You have said the actual truth.” 

Musk, the CEO of the automaker Tesla and the rocket company SpaceX, followed up his first tweet with criticism of the Anti-Defamation League, or ADL, an organization founded by Jews to oppose antisemitism. Musk has been feuding with the ADL for months over its efforts to reduce extremism on social media, a campaign that Musk says has cost X ad sales. 

On Thursday morning, Jonathan Greenblatt, the ADL’s CEO, said Musk was acting dangerously. 

“At a time when antisemitism is exploding in America and surging around the world, it is indisputably dangerous to use one’s influence to validate and promote antisemitic theories,” he wrote on X, with a screenshot of Musk’s six-word tweet. 

Accounts with histories of espousing anti-Jewish views celebrated Musk’s tweet as welcome news and as confirmation that he agrees with them “on the JQ,” short for “Jewish question,” a term used by antisemites for decades. 

“This is old-timey antisemitism with new lingo,” said A.J. Bauer, an assistant professor of journalism who studies right-wing movements and media at the University of Alabama.

IBM said Thursday it had pulled its advertisements from X. A recent investigation by the progressive organization Media Matters found that advertisements from IBM and other corporations were running on X adjacent to pro-Nazi material. 

“IBM has zero tolerance for hate speech and discrimination and we have immediately suspended all advertising on X while we investigate this entirely unacceptable situation,” the company said in a statement. A representative for IBM added that the company was investigating the Media Matters report, not Musk’s posts specifically. 

Linda Yaccarino, the CEO of X, said on the platform that antisemitism and discrimination are unacceptable, though she did not directly address Musk’s tweets or IBM’s move.

“When it comes to this platform — X has also been extremely clear about our efforts to combat antisemitism and discrimination. There’s no place for it anywhere in the world — it’s ugly and wrong. Full stop,” she wrote. X also said in an email that Media Matters’ investigation was flawed, in part because ads are designed to follow people as they browse the site, so the researcher saw the same ads multiple times in ways others might not. 

By late Thursday, Musk had not addressed the backlash, and his tweets were still online. Emails to X seeking comment from him were not immediately answered. 

Musk defended his past tweets in an interview with CNBC in May, saying he is a “prosemite,” not an antisemite.  

Musk’s latest comments came at a fraught time for Jews worldwide and in Israel. Reports of antisemitic incidents in the U.S. climbed 388% in the aftermath of Hamas’ terrorist attacks last month compared to the same period last year, according to the ADL. This week, the Biden administration announced an effort to reduce antisemitism and Islamophobia. 

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Rabbi Abraham Cooper, the director of global social action for the Simon Wiesenthal Center, an organization named for the famed Nazi hunter, said he was baffled by the way Musk uses X. 

“I don’t understand why Elon Musk, even though it’s his toy, would jump in with this kind of statement, whatever his motivation may be, that further involves him with bigots,” he said. 

“I almost feel like saying to him, ‘Grow up,’” he added. 

Experts who study antisemitism and other extremism said Musk was parroting decades-old baseless claims about Jews’ colluding with one another at the expense of others. 

“Not only is there no evidence; these have been discredited time and time again,” said Matthew Hughey, a sociology professor at the University of Connecticut who has studied white supremacy. 

Musk has 163 million followers on X, more than anyone else, so what he publishes can have a real impact on the real-world actions of others, Hughey added. 

“We should expect to see more hate crimes and rallying around this type of discourse because of his amplification,” he said. 

Musk’s tweet was the third post in a thread involving other people. The initial post, by a self-described Jewish conservative from South Florida, was a video condemning antisemitism online. It said: “You got something you want to say? Why dont you say it to our faces.”

The second person then jumped in with a multi-paragraph outline of a conspiracy theory sometimes known as the “great replacement theory,” which has been amplified by former Fox News host Tucker Carlson, among others. This person said that Jewish communities have been pushing “hatred against whites” and that Jews support “flooding” the U.S. with “hordes of minorities.” 

The person wrote that he was “deeply disinterested” in “western Jewish populations” who are now facing threats, to which Musk responded, “You have said the actual truth.” 

Musk has a long history of amplifying antisemitic conspiracy theories. In 2018, he tweeted: “Who do you think *owns* the press? Hello”; in a follow-up tweet in response to accusations of antisemitism at the time, he said he was referring only to “powerful people.” Last year, he tweeted a photo of Adolf Hitler as part of an apparent joke and welcomed back the rapper Ye, formerly known as Kanye West, to social media despite Ye’s antisemitic comments. 

“Elon Musk has been making antisemitic comments on Twitter and on other formats for many, many years,” said Bauer, of the University of Alabama. 

“When someone tells you who they are, you should listen, and he’s long been telling us that he’s an antisemite,” he said.