(CNN) Retired four-star Army Gen. Stanley McChrystal on Sunday criticized President Donald Trump for his approach to the presidency in a wide-ranging interview that saw the former top commander of the US and international forces in Afghanistan label Trump as dishonest and immoral.

"I don't think he tells the truth," McChrystal told ABC's Martha Raddatz on "This Week." When asked if he thought Trump was immoral, McChrystal responded: "I think he is."

"What I would ask every American to do is again, stand in front of that mirror and say, what are we about?," he continued. "Am I really willing to throw away or ignore some of the things that people do that 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 they're 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 in those times to take a stand," he said.

McChrystal also reacted to James Mattis' resignation from the Trump administration as Secretary of Defense earlier this month. Mattis wrote in his resignation letter that Trump had the right to a Defense Secretary whose views "better aligned" with the President's.

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