President Donald Trump speaks to members of the media before boarding Marine One on the South Lawn at the White House in Washington on Friday for a short trip to Andrews Air Force Base, Maryland, and then on to Southampton, New York, for a fundraiser. Credit: Andrew Harnik | AP

WASHINGTON — Mike Mullen, a retired U.S. Navy admiral and former chairman of the Joint Chiefs of Staff, said Sunday that President Donald Trump’s threat to revoke the security clearances of former CIA director John O. Brennan and other former officials who have been critical of him is a sign that the president is “creating a list of political enemies.”

In an appearance on “Fox News Sunday,” Mullen said that while Trump has the authority to pull the security clearances of former national intelligence and other officials, his doing so is “incredibly problematic.”

“It immediately brings back the whole concept of the ‘enemies list’ under President [Richard] Nixon,” Mullen said, adding that it was also reminiscent of the anti-communist crusade led by Joseph McCarthy in the 1950s.

Brennan has been among the president’s most vocal critics. Mullen said Sunday that he does not support the former CIA director being as critical of Trump as he has been but believes that Brennan and other former officials should not have to fear that they will be stripped of their security clearances because of their criticism.

“I am concerned about the whole issue of free speech. And as long as John is not revealing classified information that he shouldn’t, then I certainly think he has a right to speak,” Mullen said.

Earlier, 14 former CIA directors and deputy directors from Republican and Democratic administrations, as well as a former director of national intelligence, called Trump’s revocation of Brennan’s clearance a blatant attempt to “stifle free speech” and send an “inappropriate and deeply regrettable” signal to other public servants.

As criticism of Trump’s move has intensified, the president has showed no signs of backing down. According to senior administration officials, the White House has drafted documents revoking the clearances of other current and former officials who Trump has demanded be punished for criticizing him or playing a role in the investigation of Russian interference in the 2016 election.

Others on Sunday morning rallied to Trump’s defense.

National security adviser John Bolton backed the idea of a formal review to determine whether former officials should keep their security clearance and said Brennan may have “crossed the line.”

“I think a number of people have commented that he couldn’t be in the position he’s in of criticizing President Trump and his so-called collusion with Russia unless he did use classified information,” Bolton said in an interview on ABC News’ “This Week,” although he added that he has no knowledge of a single, specific instance of that.

“What I do know was when he was director of CIA, I was very troubled by his conduct, by statements he made in public and by what I thought was his politicization of the intelligence community,” the national security adviser added.

Bolton said that he did not consider a political disagreement sufficient grounds for an official to have a security clearance pulled but that violating the separation between intelligence and policy would be grounds.

He said that “senior intelligence officials, career intelligence officials who come out of the government” should “keep that wall of separation” between intelligence and policy, and that Brennan had not done that.” Bolton later added, “There is a line, and somebody can cross it.”

Bolton said it is time to review policies on security clearances for former U.S. officials.

“I think it’s certainly appropriate, in a time when we’re seeing what I believe are unprecedented leaks of highly classified information, to look at the question of how many people have clearances, how many people received this very sensitive information, both inside the government and in the case of former officials,” he said. “So, I don’t see that there would be anything wrong if it were determined to go that way to review the policies about former officials having clearances.”

In an interview on “Fox News Sunday,” Sen. Ron Johnson, R-Wisconsin, also defended Trump’s revocation of Brennan’s clearance, saying the former CIA director “abused his privilege” by denouncing Trump’s performance at a summit with Russian President Vladimir Putin in Helsinki last month as “treasonous.”

“John Brennan really did cross the line. He’s one of the leaders of the resistance movement. I understand why President Trump is pretty frustrated,” Johnson said.

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