Donald Trump has revoked the security clearance of ex-CIA chief John Brennan, denying the US president's critic of any access to sensitive information.
White House press secretary Sarah Sanders announced the decision by reading a statement from Trump.
The statement cited Brennan's "erratic conduct and behaviour".
Brennan described Trump's performance after July's summit with Russian President Vladimir Putin as being "nothing short of treasonous".
On Wednesday, Brennan tweeted at the president: "It's astounding how often you fail to live up to minimum standards of decency, civility, & probity. Seems like you will never understand what it means to be president, nor what it takes to be a good, decent, & honest person. So disheartening, so dangerous for our Nation."
Trump is also reviewing access to classified information for former FBI director James Comey, who he fired last year, and former director of national intelligence James Clapper, among others.