Defense Secretary Pete Hegseth revoked the security clearance of a former high-ranking Biden administration defense official for allegedly leaking classified information about Air Force One.

Frank Kendall, who served as President Joe Biden’s Air Force Secretary and in several high-level Pentagon posts during the Obama administration, was quoted in a New York Times article last month that stated that the Air Force One jet gifted to President Trump by the Qatari government lacks the defensive capabilities of the traditional jets that fly the president. Kendall was also quoted by The Wall Street Journal in a recent article about the Qatari-gifted aircraft.

“Safeguarding classified information is a non-negotiable duty,” Pentagon spokesman Sean Parnell wrote in a post on X. “Those who violate that trust forfeit the privilege of access and any role requiring it.” Parnell’s post didn’t specifically say what classified information Kendall released, but referenced “classified information regarding Air Force One’s capabilities.”

“I’m mystified,” Kendall said in a text message when asked for comment. “I’ve been extremely careful to not say anything that could be classified, and as far as I know I have not said anything classified.” He added, “So far no one has told me what I’m supposed to have revealed.”

Former officials often maintain security clearances after leaving government, allowing them to work on classified projects for defense contractors, serve on advisory boards or consult on other sensitive matters. Losing a security clearance could impact a person’s earning potential and marketability for jobs.

Soon after the Times published its July 9 article, the Justice Department subpoenaed several Times reporters. Federal officials said the reporters weren’t the target of the investigation. The Justice Department withdrew the subpoenas less than two weeks later.

A lack of defensive capabilities on the Qatari plane forced Trump to leave a July NATO summit in Turkey aboard an older Air Force One jet, the Journal reported. The incident came less than two weeks after the luxurious Qatari Boeing 747 began flying as Air Force One following months of upgrades. Officials haven’t detailed all of the modifications but have said the plane’s communications suite is the same as that of the older presidential planes.

Trump has since said the Qatari plane would be “maxed out” with additional upgrades, and the White House has said it would be out of service for about a month this fall for the modifications. Trump has continued to use the plane, flying it to California and Nevada this week.

Trump has previously pulled or suspended the clearance and in some cases security details of former officials that he has perceived as enemies, including more than four dozen former intelligence officials who signed a 2020 letter warning that the emails found on a laptop owned by Hunter Biden bore the hallmarks of a Russian disinformation campaign.

Those targeted by the Trump administration include Leon Panetta, who served as defense secretary and CIA director under President Barack Obama; John Bolton, who served as national security adviser to Trump during his first term; former Director of National Intelligence James Clapper, who served in the Obama administration; and retired Army Gen. Mark Milley, who served as chairman of the Joint Chiefs during Trump’s first term and under Biden.

Kendall, a onetime Raytheon executive, has consulted and served on boards between his stints in government. He recently published a book: “Lethal Autonomy: The Future of Warfare Whether We Like It or Not.”