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Why Trump revoked former CIA Director John Brennan’s security clearance.

White House press secretary Sarah Huckabee Sanders said on Wednesday that Brennan’s clearance was being revoked because of his “erratic conduct and behavior” and “frenzied commentary.” Brennan, who served under Obama from 2013 to 2017, is currently a intelligence and security commentator for NBC News. He has also become a vehement critic of President Trump’s policies and behavior since leaving the CIA last year. In July, he said that Trump’s widely condemned press conference with Russian President Vladimir Putin in Helsinki was “nothing short of treasonous.”

It’s unclear whether Brennan will have any legal recourse to keep his security clearance. The White House did not specify what mechanism it used to strip Brennan of it. What’s crystal clear is that the president is using his national-security powers to retaliate against political opponents and punish them for criticizing him. It’s no coincidence that the other officials Sanders cited for potential revocation—former FBI Director James Comey, former national security advisor Susan Rice, former Director of National Intelligence James Clapper—are among his most outspoken dissenters.

This is not an isolated phenomenon. Under Trump’s watch, the FBI has also effectively purged its upper ranks of officials who oversaw the early phases of the Russia investigation, or were corroborating witnesses to Trump’s pressure campaign against Comey before last year’s dismissal. Many of them were already the subject of constant attacks from the president on his Twitter feed. With these moves, Trump is sending a clear signal to civil servants in the American national-security apparatus: Your livelihood may depend on your personal loyalty to me.