Retired Army Gen. Stanley McChrystal, the former commander of U.S. forces in Afghanistan, sharply criticized President Trump on Sunday, calling him immoral and untruthful and taking aim at his foreign policy decisions.

In an interview on ABC News’s “This Week,” McChrystal told host Martha Raddatz of Trump, “I don’t think he tells the truth.” The general also responded affirmatively when asked whether he believes Trump is immoral.

McChrystal said that contrary to Trump’s claim, the Islamic State militant group has not yet been defeated.

“I don’t believe ISIS is defeated. I think ISIS is as much an idea as it is a number of ISIS fighters. There’s a lot of intelligence that says there are actually more ISIS fighters around the world now than there were a couple of years ago,” he said.

The president tweeted this month that “we have defeated ISIS in Syria” and abruptly announced plans to withdraw all U.S. forces from that country, against the counsel of his top advisers.

The decision – along with Trump’s directive days later to withdraw nearly half of the more than 14,000 troops deployed to Afghanistan – prompted the resignation of Defense Secretary Jim Mattis.

McChrystal, who recently co-wrote a book on leadership, on Sunday praised Mattis as “selfless” and “committed” and said his departure should give Americans pause. He also decried Trump’s decision on Afghanistan, saying it effectively traded away U.S. leverage against the Taliban and “rocked (the Afghan people) in their belief that we are allies that can be counted on.”

McChrystal has been outspoken in his criticism of Trump earlier, as well. Last month, when the president pushed back against criticism from retired Adm. William McRaven by saying the decorated Navy SEAL and Special Operations commander should have caught Osama bin Laden more quickly, McChrystal rallied to McRaven’s defense, saying there has to be a “confidence” in the “basic core values” of the country’s leaders.

Sen. Lindsey Graham, R-S.C., one of Trump’s closest allies on Capitol Hill, said ahead of a lunch with the president on Sunday that he would try to get him to reconsider his decision to withdraw troops from Syria.

“I’m asking the president to make sure we have troops there to protect us,” Graham said on CNN’s “State of the Union.”

But after the lunch, Graham said that he had come around to Trump’s point of view on the troop withdrawal, which he described as “a pause situation.”

In Sunday’s interview, McChrystal said he would decline if asked to work in the Trump administration.

“I’d say no. It’s important for me to work for people who I think are basically honest, who tell the truth as best they know it,” he said.