President Donald Trump took on retired four-star Army Gen. Stanley McChrystal today, saying he "got fired like a dog" and is known for his "big, dumb mouth" -- comments that come on the heels of the general criticizing the president.

“General” McChrystal got fired like a dog by Obama. Last assignment a total bust. Known for big, dumb mouth. Hillary lover!" Trump tweeted.

The president was reacting to McChrystal's interview with ABC's Martha Raddatz on "This Week" Sunday, where he said the commander-in-chief is dishonest and immoral.

“I don’t think he tells the truth,” McChrystal said when asked if he believes the president is a liar.

“Is Trump immoral, in your view?” Raddatz asked.

“I think he is,” he said.

McChrystal said he couldn't tell any of Trump's supporters "that they are wrong," but added, "What I would ask every American to do is ... stand in front of that mirror and say, 'What are we about? Am I really willing to throw away or ignore some of the things that people do that are -- are pretty unacceptable normally just because they accomplish certain other things that we might like?'

"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."

McChrystal, a 34-year veteran of the U.S. Army, served as the head of the Joint Special Operations Command from 2003 to 2008 and later assumed command of all international forces in Afghanistan in June 2009.

President Barack Obama relieved McChrystal of that command in June 2010 after Rolling Stone published controversial comments McChrystal made in an interview about the administration.

In doing so, Obama still praised the general's "deep intelligence" and "love of the country."