WASHINGTON – President Donald Trump blasted his former Defense secretary on Wednesday, claiming he "essentially" fired James Mattis.

"What's he done for me?" Trump asked during a Cabinet meeting that reporters observed for about 90 minutes. Trump specifically criticized the former top military aide on Afghanistan, suggesting U.S. military policy was "not too good" under his command.

"I’m not happy with what he’s done in Afghanistan," Trump said. "As you know, President Obama fired him and essentially so did I."

Mattis, in fact, resigned last month, citing disagreements with Trump on Syria and global alliances in a lengthy resignation letter. Trump announced on Dec. 23 that Mattis would leave on Jan. 1 rather than the previously announced resignation date of Feb. 28.

More:Defense Secretary Jim Mattis leaving his job after clash with Trump over Syria

Also:President Trump orders Defense Secretary James Mattis to leave immediately

Trump was set to meet with congressional leaders Wednesday to discuss the partial government shutdown, and most of his remarks focused on that issue. The president said he is sticking by a demand for $5 billion in funding for a proposed border wall.

Trump also touched on several other topics:

Flanked by acting Defense Secretary Patrick Shanahan and acting Interior Secretary David Bernhardt, Trump touted progress with North Korea. He said he had received a letter from North Korean leader Kim Jong Un and said there would have been a “big fat war in Asia” if he had not met with Kim in June. "We'll probably now have another meeting," Trump said. "He'd like to meet, I'd like to meet."

The president pushed back on criticism from Utah Sen.-elect Mitt Romney, who recently wrote that Trump “has not risen to the mantle of the office.” Trump said he wished Romney "could be more of a team player." Trump added that "I endorsed him and he thanked me profusely.”

Trump discussed the wild swings in the stock market in recent days. He described the turbulence as a "little glitch in the stock market last month” and predicted markets would stabilize after he finishes negotiating new trade deals.

The president declined to be pinned down on a timeline for U.S. withdrawal from Syria, which he announced Dec. 19. "Syria was lost long ago," the president said. "We're talking about sand and death. We’re not talking about vast wealth."

Contributing: Tom Vanden Brook