Sen. Rand Paul (R-Ky.) has called for the use of lie detector tests to identify the senior administration official who wrote the anonymous New York Times op-ed and who criticized President Donald Trump.

“I think it’s not unprecedented for people with security clearances to be asked to, whether or not they were revealing things against the law under oath and also by lie detector,” Paul said on Thursday. “We use a lie detector test routinely for CIA agents and FBI agents. I think if you have a security clearance in the White House, I think it would be acceptable to use a lie detector test and ask people whether they are talking to the media against the policy of the White House.”

He continued, “This could be very dangerous if the person who is talking to the media is actually revealing national security secrets. So, yes, I think we need to get to the bottom of it.”

Other people around the president also considering asking senior officials suspected of writing the column to sign sworn affidavits that could be used against them in court.

The op-ed, written by a senior Trump administration official who says they are part of an internal “resistance” working to thwart parts of Trump’s agenda and block his worst impulses, was published amid questions of President Donald Trump’s fitness and his control over his administration.

Alvin S. Felzenberg, a presidential historian and a professor at the University of Pennsylvania’s Annenberg School of Communications, told The New York Times it is unusual for a libertarian senator to favor a lie detector.

“For a libertarian senator to favor lie detector tests, surveillance of people working for the government, and the other things he’s called for, I find it a paradox,” Felzenberg said. “Another libertarian is [Sen. Jeff] Flake, and he’s not saying any of these things and he came from the Goldwater Institute, which is very libertarian.”

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Trump and Paul have forged a personal friendship, outside of Washington.

“Sen. Rand Paul considers President Trump a personal friend. Their relationship predates either one of them running for the presidency. From increased engagement around the world, to cutting regulations and taxes at home, to ending futile nation-building exercises around the world, they have often found areas of mutual agreement,” said Sergio Gor, Paul’s deputy chief of staff.