Trump announced on Wednesday that he was stripping Brennan, who has been an outspoken critic of the President, of his security clearance and accused the former Central Intelligence Agency director of "lying" and giving "increasingly frenzied commentary" on television.
Twelve former senior intelligence officials have issued a statement on what they call "the ill-considered and unprecedented remarks and actions by the White House regarding the removal of John Brennan's security clearances".
In his op-ed, Brennan characterized Trump's action as "politically motivated" and said it was "an attempt to scare into silence others who might dare to challenge him".
Two of those who signed the statement - former director of national intelligence James Clapper and former CIA Director Michael Hayden - are, according to Trump, on a list of people who could lose their clearance. "I suspect I'll be taking it away very quickly", Trump told journalists.
"I think this is just another example of Mr. Trump trying to frighten and intimidate others, but I can tell you ... these are not the type of people who are going to be bullied or intimidated by someone of the likes of Mr. Trump", Brennan said.
"So I think it's something that had to be done", he said.
These file photos, top row from left, are former CIA Director Michael Hayden, former FBI Director James Comey, former acting FBI director Andrew McCabe and former national security adviser Susan Rice. Several of them have said they no longer have clearances. It certainly doesn't appear as if Trump initiated any kind of investigation or process before terminating Brennan's clearance.
The White House did not immediately return a request for comment.
"I will be introducing an amendment next week to block the President from punishing and intimidating his critics by arbitrarily revoking security clearances", Warner tweeted. Ohr is still in the Justice Department, and was reportedly meeting with Christopher Steele, the British spy who complied the famous "dossier" on Trump's alleged ties to Russian Federation. The others are former director of national intelligence James Clapper Jr.; former CIA and Federal Bureau of Investigation directors Michael Hayden and James Comey; Obama national security adviser Susan Rice; former Federal Bureau of Investigation officials Andrew McCabe, Lisa Page and Peter Strzok; and former acting attorney general Sally Yates.
The extreme action of revoking security clearances is one more instance of Donald Trump undertaking measures that no other president has done, leaving legal analysts in question about whether the action is actually within his authority.
DiGenova said that if Clinton won, "we would know [nothing]" about the handling of Christopher Steele's dossier and alleged bias within the FBI during the Clinton email probe and Trump-Russia investigation. "I've never respected him", Trump said.
Brennan, a fierce critic of the president, has been firing back at Mr. Trump. "This is the first time in 38 years I haven't had a security clearance".
But a few days after Comey was dismissed, Trump told NBC's Lester Holt in an interview that he was really thinking of "this Russian Federation thing" when he fired Comey.