GenStanleyMcCrystal
© Steven Senne/APGeneral Stanley McCrystal
President Donald Trump lashed out Tuesday at a retired army general who had been critical of him and his decision to withdraw U.S. troops from Syria.

In a New Year's Day post to Twitter, Trump said retired Gen. Stanley McChrystal is "known for [a] big, dumb mouth" and that he "got fired like a dog by Obama." The president identified McChrystal as a "general," apparently deriding the former military official by placing his title in quotes, and called him a "Hillary lover."

Trump's critisicim of McChrystal came after the retired general told Martha Raddatz on ABC's This Week that the president is immoral and does not tell the truth.

"If we want to be governed by someone we wouldn't do a business deal with because their - their background is so shady, if we're willing to do that, then that's in conflict with who I think we are. And so I think it's necessary at those times to take a stand," the retired general said.

McChrystal also said the president's decision to withdraw U.S. troops from Syria would lead to instability in the region. "If you pull American influence out, you're likely to have greater instability, and of course it'll be much more difficult for the United States to try to push events in any direction," he told ABC News.

McChrystal rose to public prominence as a military officer during the administration of President Barack Obama, who tasked the four-star Army general with leading U.S. forces in Afghanistan. McChrystal resigned in 2010 amid the publication of a Rolling Stone magazine article in which he and aides made comments critical of Obama administration officials, including Vice President Joe Biden.