Speaking on Friday on MSNBC’s Morning Joe, Mr Brennan referred to “a virtual decapitation of the intelligence community”.
His comments follow reports that Donald Trump had deliberately interfered in the work of the intelligence community by attempting to prevent the flow of intelligence to Congress and by removing key figures from their leadership roles and replacing them with loyalists.
On Thursday Mr Brennan tweeted: “We are now in a full-blown national security crisis. By trying to prevent the flow of intelligence to Congress, Trump is abetting a Russian covert operation to keep him in office for Moscow's interests, not America's.”
He referred to a report in The New York Times that says last week members of the House Intelligence Committee were briefed that Russia is actively meddling in the 2020 election in order to keep Donald Trump in office.
The briefing was provided by Shelby Pierson, an aide to Joseph Maguire, Acting Director of National Intelligence, and the election security czar.
When President Trump found out about the briefing, he was livid at the prospect that committee chair Adam Schiff could “weaponise” the intelligence against him, according to the The New York Times.
We are now in a full-blown national security crisis. By trying to prevent the flow of intelligence to Congress, Trump is abetting a Russian covert operation to keep him in office for Moscow’s interests, not America’s. https://t.co/Vj6lUV5ZNu
— John O. Brennan (@JohnBrennan)
The Washington Post reports that Mr Trump erroneously believed that only Mr Schiff was briefed on the information. A committee official confirmed that committee members from both parties attended the briefing.
The president, angry at Mr Maguire and his staff for what he saw as disloyalty, announced that he is being replaced by Trump loyalist Richard Grenell, currently US Ambassador to Germany.
Mr Brennan expressed his concern at the removal of Mr Maguire and his deputy, Andrew Holman, a senior CIA officer. He described Mr Grenell as someone with no experience or credentials when it comes to intelligence.
Members of the intelligence community are said to be “aghast” at the situation.
In the midst of the outcry over Mr Grenell’s appointment, Mr Trump reiterated in a tweet that he was being appointed in an ‘acting’ capacity and added that he would be “nominating a terrific candidate for the job very soon”.
Continuing his comments on MSNBC, Mr Brennan, who served as CIA director from 2013 to 2017 and has worked with six different presidents, said: “What we are seeing now is such an anomaly, such an aberration from what we have seen in the past about the importance of the independence of the intelligence community.”
He implored those working in the intelligence community to continue to do their jobs that are so vital to national security.