Former U.S. Central Intelligence Agency director John Brennan says he believes President Donald Trump revoked his security clearance because he wants to "silence others who might dare to challenge him."

In an opinion piece published Thursday in The New York Times, Brennan contended that Trump "clearly has become more desperate to protect himself and those close to him, which is why he made the politically motivated decision to revoke my security clearance."

Brennan, who was the CIA director during the second White House term of former President Barack Obama from 2013 to 2017, said that Trump's claims that "no collusion" occurred between his 2016 presidential campaign and Russia "are, in a word, hogwash."

"The only questions that remain are whether the collusion that took place constituted criminally liable conspiracy, whether obstruction of justice occurred to cover up any collusion or conspiracy, and how many members of 'Trump Incorporated' attempted to defraud the government by laundering and concealing the movement of money into their pockets," said Brennan, who often has been highly critical of Trump on cable news talk shows.

White House press secretary Sarah Sanders calls on White House press secretary Sarah Sanders calls on a member of the media during the daily press briefing at the White House, Aug. 15, 2018. Sanders announced that President Donald Trump will remove the security clearance from former Obama administration CIA director John Brennan, a vocal critic of the president, and the administration will be reviewing the security clearances for a number of other former officials. White House press secretary Sarah Sanders calls on a member of the media during the daily press briefing at the White House, Aug. 15, 2018. Sanders announced that President Donald Trump will remove the security clearance from former Obama administration CIA director John Brennan, a vocal critic of the president, and the administration will be reviewing the security clearances for a number of other former officials.

Trump, in an interview with The Wall Street Journal, said he believes Brennan is one of the people responsible for special counsel Robert Mueller's ongoing 15-month probe into links between Trump's campaign and Russia and whether Trump, as president, obstructed justice by trying to thwart the investigation.

Trump, often critical of the Mueller investigation, told the newspaper it is a "rigged witch hunt ... a sham."

"And these people led it," Trump said, referring to Brennan and nine other past and current government security officials whose clearances he is considering revoking.

"So, I think it's something that had to be done," Trump said of revoking Brennan's clearance.

Other names

Trump said he does not trust "many of those people on that list" and does not think they are "good people."

On his Twitter account, Trump reposted several comments supporting his revocation of Brennan's clearance, including one from Sean Hannity, a conservative Fox News television host.

"I'd strip the whole bunch of them," Hannity said. "They're all corrupt."

“I’d strip the whole bunch of them. They’re all corrupt. They’ve all abused their power. They’ve all betrayed the American people with a political agenda. They tried to steal and influence an election in the United States.” @seanhannity — Donald J. Trump (@realDonaldTrump) August 16, 2018

The White House said Wednesday that security clearances are under review for former U.S. National Intelligence director James Clapper, former FBI director James Comey, former Obama administration National Security adviser Susan Rice, former National Security Agency director Michael Hayden and former Deputy Attorney General Sally Yates.

"Security clearances for those who still have them may be revoked, and those who have already lost their security clearance may not be able to have it reinstated," White House spokeswoman Sarah Sanders told reporters, reading a statement in the president's name.

These file photos, top row from left are former CI 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. Bottom row from left are former FBI Deputy Assistant Director Peter Strzok, former Deputy Attorney General Sally Yates and former National Intelligence Director James Clapper. President Donald Trump acted Aug. 15, 2018, on a threat and revoked the security clearance of former CIA Director John Brennan, citing a constitutional responsibility to protect classified information. Trump says he is reviewing security clearances for nine other individuals, including the eight pictured. 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. Bottom row from left are former FBI Deputy Assistant Director Peter Strzok, former Deputy Attorney General Sally Yates and former National Intelligence Director James Clapper. President Donald Trump acted Aug. 15, 2018, on a threat and revoked the security clearance of former CIA Director John Brennan, citing a constitutional responsibility to protect classified information. Trump says he is reviewing security clearances for nine other individuals, including the eight pictured.

?'I will not relent'

Sanders, responding to reporters' questions, denied that Brennan and others are being singled out because they are critics of Trump.

The president's statement accused Brennan of "erratic conduct and behavior" that "has tested and far exceeded the limits of any professional courtesy that may have been due to him." It also accuses Brennan of "a history that calls into question his objectivity and credibility."

Brennan has been vocal in his attacks on Trump, at one point saying that Trump's performance at a joint news conference last month with Russian President Vladimir Putin in Helsinki was "nothing short of treasonous."

Brennan on Twitter described Trump's action on Wednesday as part of a broader effort "to suppress freedom of speech and punish critics."

Brennan, who spent 25 years with the CIA, concluded: "My principles are worth far more than clearances. I will not relent."