Former CIA Director John Brennan said Thursday that President Trump yanked his security clearance because his campaign colluded with the Russians to sway the 2016 election and is now desperate to end the special counsel's investigation.

In an opinion piece in The New York Times, Mr. Brennan cites press reports and Mr. Trump's own goading of Russia during the campaign to find Democrat Hillary Clinton's missing emails.

Trump himself drew a direct connection between the revocation of Brennan's clearance and the Russia probe, telling The Wall Street Journal the investigation is a "sham," and "these people led it!"

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

Brennan wrote that Trump's claims of no collusion with Russia are "hogwash" and that the only question remaining is whether the collusion amounts to a "constituted criminally liable conspiracy."

"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 in an attempt to scare into silence others who might dare to challenge him," he wrote.

Brennan's loss of a security clearance was an unprecedented act of retribution against a vocal critic and politicizes the federal government's security clearance process. Former CIA directors and other top national security officials are typically allowed to keep their clearances, at least for some period, so they can be in a position to advise their successors and to hold certain jobs.

Trump said Wednesday he is reviewing the security clearances of several other former top intelligence and law enforcement officials, including former FBI Director James Comey. All are critics of the president or are people whom Trump appears to believe are against him.

Democrats called it an "enemies list," a reference to the Nixon White House, which kept a list of President Richard Nixon's political opponents to be targeted with punitive measures.

There was no reference to the Russia probe in a White House statement Wednesday in which Trump denounced Brennan's criticism of him and spoke of "the risks posed by his erratic conduct and behavior." The president said he was fulfilling his "constitutional responsibility to protect the nation's classified information."

Trump, his statement read by his press secretary, accused Brennan of having "leveraged his status as a former high-ranking official with access to highly sensitive information to make a series of unfounded and outrageous allegations, wild outbursts on the internet and television about this administration."

"Mr. Brennan's lying and recent conduct characterized by increasingly frenzied commentary is wholly inconsistent with access to the nations' most closely held secrets," Trump said.

In the Journal interview, Trump said he was prepared to yank Brennan's clearance last week but that it was too "hectic." The president was on an extended working vacation at his New Jersey golf club last week.

Brennan has indeed been deeply critical of Trump's conduct, calling his performance at a press conference last month with Russian President Vladimir Putin in Finland "nothing short of treasonous."

Brennan said Wednesday that he had not heard from the CIA or the Office of the Director of National Intelligence that his security clearance was being revoked, but learned it when the White House announced it. There is no requirement that a president has to notify top intelligence officials of his plan to revoke a security clearance.

Trump's statement said the Brennan issue raises larger questions about the practice of allowing former officials to maintain their security clearances, and said that others officials' were under review.

They include Mr. Comey; James Clapper, the former director of national intelligence; former CIA Director Michael Hayden; former national security adviser Susan Rice; and Andrew McCabe, who served as Trump's deputy FBI director until he was fired in March.

Also on the list: fired FBI agent Peter Strzok, who was removed from the Russia investigation over anti-Trump text messages; former FBI lawyer Lisa Page, with whom Mr. Strzok exchanged messages; and senior Justice Department official Bruce Ohr, whom Trump recently accused on Twitter of "helping disgraced Christopher Steele 'find dirt on Trump.' "

Mr. Ohr was friends with Mr. Steele, the former British intelligence officer commissioned by an American political research firm to explore Trump's alleged ties with the Russian government. He is the only current government employee on the list.

At least two of the former officials, Comey and Mr. McCabe, do not currently have security clearances, and none of the eight receive intelligence briefings. Trump's concern apparently is that their former status gives special weight to their statements, both to Americans and foreign foes.

Former intelligence officials said Trump has moved from threatening to revoke security clearances of former intelligence officials who have not been involved in the Russia investigation to former officials who did work on the probe. They spoke on condition of anonymity to share private conversations Trump has had with people who have worked in the field.

The CIA referred questions to the White House.

Mr. Clapper, reacting on CNN, called Trump's actions "unprecedented," but said he didn't plan to stop speaking out.

Sarah Huckabee Sanders, Trump's press secretary, insisted the White House wasn't targeting only Trump critics. But Trump did not order a review of the clearance held by former national security adviser Mike Flynn, who was fired from the White House for lying to Vice President Mike Pence about his conversations with Russian officials and later pleaded guilty to lying to the FBI.

Democrats, and even some Republicans, lined up to denounce the president's move, with House Minority Leader Nancy Pelosi of California, slamming it as a "stunning abuse of power." And California Rep. Adam Schiff, the ranking Democrat on the House intelligence committee, tweeted, "An enemies list is ugly, undemocratic and un-American."

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Several Republicans also weighed in, with Sen. Bob Corker (R) of Tennessee, saying, "Unless there's something tangible that I'm unaware of, it just, as I've said before, feels like a banana republic kind of thing."

This story was reported by The Associated Press. Associated Press writers Deb Riechmann, Zeke Miller, Lisa Mascaro, and Matthew Daly contributed to this report.