President Trump Donald John TrumpHR McMaster says president's policy to withdraw troops from Afghanistan is 'unwise' Cast of 'Parks and Rec' reunite for virtual town hall to address Wisconsin voters Biden says Trump should step down over coronavirus response MORE on Thursday tore into his former chief of staff John Kelly John Francis KellyMORE, deriding his job performance and accusing him of breaching decorum after Kelly openly criticized the president's rhetoric and decisionmaking.

Trump lashed out at Kelly after reports circulated that his former chief of staff and Homeland Security secretary defended migrants, the press and Lt. Col. Alexander Vindman Alexander VindmanImpeachment witness Alexander Vindman calls Trump Putin's 'useful idiot' The Hill's Morning Report - Sponsored by The Air Line Pilots Association - Trump, Biden renew push for Latino support Strzok: Trump behaving like an authoritarian MORE, who was reassigned from his post after testifying against Trump in the impeachment inquiry.

"When I terminated John Kelly, which I couldn’t do fast enough, he knew full well that he was way over his head. Being Chief of Staff just wasn’t for him," Trump tweeted. "He came in with a bang, went out with a whimper, but like so many X’s, he misses the action & just can’t keep his mouth shut, which he actually has a military and legal obligation to do."

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The president went on to claim Kelly's wife told him the former administration official and four-star general respected him "greatly" and "will only speak well of" him.

....which he actually has a military and legal obligation to do. His incredible wife, Karen, who I have a lot of respect for, once pulled me aside & said strongly that “John respects you greatly. When we are no longer here, he will only speak well of you.” Wrong! — Donald J. Trump (@realDonaldTrump) February 13, 2020

Trump nominated Kelly to serve as his Homeland Security secretary before appointing him chief of staff in July 2017. He stayed on in that role for roughly 17 months, stepping down at the end of 2018.

Trump has a tendency to lash out at former administration officials who openly criticize him, having tweeted angrily about former Secretary of State Rex Tillerson Rex Wayne TillersonGary Cohn: 'I haven't made up my mind' on vote for president in November Kushner says 'Alice in Wonderland' describes Trump presidency: Woodward book Conspicuous by their absence from the Republican Convention MORE, former national security adviser John Bolton John BoltonDiplomacy with China is good for America The Hill's Morning Report - Sponsored by The Air Line Pilots Association - Pence lauds Harris as 'experienced debater'; Trump, Biden diverge over debate prep DOJ launches probe into Bolton book for possible classified information disclosures MORE and former communications director Anthony Scaramucci Anthony ScaramucciFormer DeVos chief of staff joins anti-Trump group Scaramucci to Lemon: Trump 'doubling down' on downplaying virus 'should scare' viewers Sunday shows - Leaked audio of Trump's sister reverberates MORE, among others.

Kelly appeared Wednesday night at a Drew University event in New Jersey, where he laid out a number of disagreements with Trump's policies and comments.

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Kelly defended Vindman, saying he acted properly in reporting his concerns with Trump's July 25 call with the Ukrainian president. He said the media is "not the enemy of the people," dismissing an attack frequently deployed by the president. Kelly described migrants as "overwhelmingly good people," an implicit rebuke of Trump's warnings of dangerous caravans and the need to curb immigration.

Kelly's tenure was marked by his turbulent relationship with Trump. Kelly tried to rein in some of the president's more impulsive behavior and curb leaks within the White House, but the administration continued to struggle with infighting and controversy.

His successor, Mick Mulvaney Mick MulvaneyMick Mulvaney to start hedge fund Fauci says positive White House task force reports don't always match what he hears on the ground Bottom line MORE, has been acting chief of staff for more than 400 days. Mulvaney has in the past been critical of Kelly's approach to the job, saying it hurt morale.