U.S. President Donald Trump on Friday called on the U.S. Justice Department to investigate the New York Times after the news outlet published a column this week by an anonymous administration official questioning his fitness for office.

Trump also said he was considering taking action against the Times, whose shares moved briefly lower after his comments were made public.

“We’re going to see. I’m looking at that right now,” Trump told reporters aboard Air Force One.

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Attorney General Jeff Sessions “should be investigating who the author of that piece was because I really believe it’s national security.”

Trump did not indicate what sort of action he was considering against the Times and it was unclear what legal grounds he could act on.

A Justice Department spokeswoman said the department does not confirm or deny investigations. The Times could not be immediately reached for comment.

A number of top Trump advisers have disavowed the piece, which was published on Wednesday without a name in what the Times said was a rare but necessary move to protect the writer.

In the column, the writer slammed Trump’s “amorality” and leadership style. The official said there were a number of U.S. officials who were part of an “quiet resistance” inside the administration who was “working diligently from within to frustrate parts of his agenda and his worst inclinations.”

Trump regularly attacks the media for focusing on negative news about his administration and decries what he perceives as “fakes news.” He repeated on Air Force One that he believes libel laws should be strengthened.

Earlier this week the Justice Department said is set a meeting with state attorneys general to discuss concerns social media platforms are stifling conservative voices.