Former CIA Director John Brennan John Owen BrennanJournalism or partisanship? The media's mistakes of 2016 continue in 2020 Comey on Clinton tweet: 'I regret only being involved in the 2016 election' Ex-CIA Director Brennan questioned for 8 hours in Durham review of Russia probe MORE praised Sen. John McCain John Sidney McCainAnalysis: Biden victory, Democratic sweep would bring biggest boost to economy The Memo: Trump's strengths complicate election picture Mark Kelly: Arizona Senate race winner should be sworn in 'promptly' MORE after the Arizona Republican's death, calling him a “man of tremendous courage, patriotism, and integrity.”

“A man of tremendous courage, patriotism, and integrity, Senator John McCain will be remembered by history as one of our country’s greatest heroes,” Brennan tweeted. “His life of service and his strong decency and respect toward others should serve as a shining example for all Americans.”

A man of tremendous courage, patriotism, and integrity, Senator John McCain will be remembered by history as one of our country’s greatest heroes. His life of service and his strong decency and respect toward others should serve as a shining example for all Americans. — John O. Brennan (@JohnBrennan) August 26, 2018

McCain, a giant in the Senate and former GOP presidential nominee who was respected by lawmakers and political leaders of both parties, died Saturday at the age of 81 after a battle with brain cancer.

Brennan, a frequent and harsh critic of the Trump administration, had his security clearance revoked by President Trump Donald John TrumpSteele Dossier sub-source was subject of FBI counterintelligence probe Pelosi slams Trump executive order on pre-existing conditions: It 'isn't worth the paper it's signed on' Trump 'no longer angry' at Romney because of Supreme Court stance MORE earlier this month in a controversial move that was widely panned by dozens of current and former national intelligence officials.

Brennan praised McCain in an interview Friday while criticizing Republicans for not taking a stronger stance against Trump.

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"I got into some real donnybrook fights with John McCain over policy," Brennan told HBO host Bill Maher. "I never once questioned his integrity and his interest in doing what is best for this country."

“But since John McCain has left the Hill, the Republican spines have gone with him," he added. "And there needs to be some reckoning in the Republican Party, [because] we can't allow this to go on."

McCain was also a harsh critic of Trump, and reportedly did not want the current president to attend his funeral.

Trump, who frequently mocked McCain, even into his final weeks, lowered the White House flags to half-staff on Saturday following the news of McCain’s death.

"My deepest sympathies and respect go out to the family of Senator John McCain,” Trump tweeted. “Our hearts and prayers are with you!"