President Trump Donald John TrumpBarr criticizes DOJ in speech declaring all agency power 'is invested in the attorney general' Military leaders asked about using heat ray on protesters outside White House: report Powell warns failure to reach COVID-19 deal could 'scar and damage' economy MORE on Tuesday lashed out at retired Gen. Stanley McChrystal with a string of personal attacks after the former leader of U.S. operations in Afghanistan called the president "immoral" and dishonest.

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The president said former President Obama fired McChrystal "like a dog" while quoting a tweet from Fox News host Laura Ingraham that shared a post from a conservative website founded by her that recapped McChrystal's weekend comments.

" 'General' McChrystal got fired like a dog by Obama. Last assignment a total bust. Known for big, dumb mouth. Hillary lover!" Trump tweeted on New Year's Day.

“General” McChrystal got fired like a dog by Obama. Last assignment a total bust. Known for big, dumb mouth. Hillary lover! https://t.co/RzOkeHl3KV — Donald J. Trump (@realDonaldTrump) January 1, 2019

The retired four-star Army general said on ABC's "This Week" that he would not work for the Trump administration if asked, citing the president's dishonesty.

"It’s important for me to work for people who I think are basically honest, who tell the truth as best they know it," McChrystal said.

"I don’t think he tells the truth," he added.

McChrystal has previously been critical of Trump's policies and rhetoric.

He has questioned Trump's decision to send troops to the southern border and has expressed concern over the president's repeated criticism of former military leaders, such as retired Adm. William McRaven.

The president in November derided McRaven, who oversaw the mission that killed Osama bin Laden, as a "Hillary Clinton Hillary Diane Rodham ClintonBarr criticizes DOJ in speech declaring all agency power 'is invested in the attorney general' Virginia Democrat blasts Trump's 'appalling' remark about COVID-19 deaths in 'blue states' The Hill's Campaign Report: Biden asks if public can trust vaccine from Trump ahead of Election Day | Oklahoma health officials raised red flags before Trump rally MORE fan."

Trump used the same line of attack on McChrystal on Tuesday. McChrystal has in the past praised Clinton's work as secretary of State, but had stopped short of formally endorsing her presidential bid against Trump in 2016.

McChrystal led U.S. forces in Afghanistan from 2009 to 2010. He resigned after critical remarks he made about Vice President Joe Biden and other civilian leaders were published in Rolling Stone.

Trump is currently in search of a full-time Defense secretary after James Mattis James Norman MattisBiden courts veterans amid fallout from Trump military controversies Trump says he wanted to take out Syria's Assad but Mattis opposed it Gary Cohn: 'I haven't made up my mind' on vote for president in November MORE resigned, effective Tuesday. Mattis's resignation came after Trump announced plans to withdraw U.S. forces from Syria.

Trump appointed Patrick Shanahan as acting Defense secretary.