Tech billionaire Elon Musk continues to push a right-wing conspiracy theory about the Biden administration “importing voters” by transporting undocumented immigrants into the country, and in a recent post, goes so far as to suggest that immigrants may be orchestrating a terror attack against the U.S.

“This administration is both importing voters and creating a national security threat from unvetted illegal immigrants,” he wrote on X late Monday. “It is highly probable that the groundwork is being laid for something far worse than 9/11. Just a matter of time.”

Musk included a screenshot of a headline of a Daily Mail story centered on a report issued Monday from the Center for Immigration Studies, an organization that has pushed for strict limits on immigration, about Customs and Border Protection declining to disclose the airports where undocumented immigrants are arriving via its CBP One app due to “operational vulnerabilities.” The federal government has been guarded with information regarding such flights in the past, as WHYY reported, in part to protect the privacy of those on board, including children.

The conspiracy theory about the administration covertly flying undocumented immigrants into the U.S. as part of a vast ploy to increase voter turnout for Democrats has swirled among the right-wing media and Republicans since at least 2021. Some of the flights, operated for the Office of Refugee Resettlement, are part of a long-standing practice to relocate minors and unite them with caretakers — a practice that was also common under former President Donald Trump. The more conspiratorial aspects have been repeatedly debunked by CNN, The Washington Post and PolitiFact.

The CBP One app allows migrants to apply for an appointment to be vetted and processed by U.S. immigration authorities. CBS News reported that between January 2023 and February this year, almost 450,000 people have been processed by U.S. immigration officials after making an appointment on the app. More than 64.3 million appointment requests have been made from migrants in Mexico alone, according to CBS.

Musk, who immigrated to the U.S. himself, is partial to anti-immigration sentiment. He has promoted what the Post likened to “great replacement”-adjacent rhetoric, repeatedly claiming that Democrats want undocumented immigrants to enter the country as a way to gain more votes. (For the record, Democratic lawmakers have increasingly signaled that they are open to harsh anti-immigration policies for which they’ve previously criticized their GOP counterparts.)

Musk now appears to have escalated this already racist conspiracy about migrants into evidence-free fearmongering that they could be plotting a terror attack.