ABOARD AIR FORCE ONE — President Trump called Friday for the Justice Department to investigate the anonymous author of an op-ed depicting a “resistance” inside the government and said he is considering taking legal action against the New York Times for publishing it.

The column, published online Wednesday, was written by someone the Times identified only as a senior official in the Trump administration. It depicts a “two-track presidency” in which some top staffers make up a “resistance” force working to thwart the president’s “misguided impulses” in the name of protecting the nation.

“We’re going to take a look at what he had, what he gave, what he’s talking about, also where he is right now,” Trump told reporters. If the anonymous author has a high-level security clearance, the president added, “and he goes into a high-level meeting concerning China or Russia or North Korea or something, I don’t want him in those meetings.”

Traveling aboard Air Force One to Fargo, North Dakota, from Billings, Montana, Trump told reporters that there is a national security imperative to root out the anonymous author, whom he called “a sick person.” He said Attorney General Jeff Sessions – who he has long criticized publicly in especially harsh terms – should use the investigative powers of the Justice Department to determine who authored the column.

“I would say Jeff should be investigating who the author of that piece was because I really believe it’s national security,” Trump said.

Asked if he trusts his White House staffers, Trump said, “I do, but what I do now is I look around the room. I say, ‘Hey, if I don’t know somebody … ‘ ” He added, “We have a really well-run, smooth-running White House. It’s a well-oiled machine. It is running beautifully.”

Trump made his comments in a 25-minute question-and-answer session with reporters traveling with him.

Trump also denied one of the more shocking anecdotes in Bob Woodward’s new book, “Fear.” Woodward reports that Gary Cohn, then the White House’s chief economic adviser, plucked a letter off Trump’s desk that the president intended to sign that would have terminated the trade agreement between the United States and South Korea. In his book, Woodward publishes a picture of the unsigned letter.

Woodward also reports that Cohn took another memo off Trump’s desk that, had the president signed it, would have initiated the process for the United States to withdraw from the North American Free Trade Agreement with Canada and Mexico.

But Trump denied Woodward’s reporting, calling it a “phony story.”

“Gary Cohn, if he ever took a memo off my desk, I would have fired him in two seconds,” Trump said. “He would have been fired so fast. He would have been fired within the first second that it took place.”

In the session with reporters, Trump also weighed in on a number of other topics, including special counsel Robert S. Mueller III’s probe of Russian interference in the 2016 election.

The president said he would be willing to submit to an interview with Mueller under certain circumstances but considers doing so a waste of time and is afraid of being caught committing perjury.

“I’d do it, but under certain circumstances,” Trump said. “It’s a big waste of time.”

For months now, Trump’s personal attorneys have been negotiating the terms of a possible interview with Mueller, who is eager to question the president as a witness on a range of topics. Mueller and his team are investigating possible collusion between the Russians and Trump campaign as well as the president’s possible obstruction of justice.

Trump also told reporters that he was expecting to receive a letter in the coming days from North Korean leader Kim Jong Un, which would be sent through Secretary of State Mike Pompeo.

Trump expressed optimism about the state of negotiations over Kim’s government abandoning its nuclear weapons program, even though Trump called off Pompeo’s planned trip to North Korea last month because Kim had not demonstrated sufficient progress toward denuclearizing.