CNN White House correspondent Jim Acosta said Friday that a source has told him that President Donald Trump is furious about Defense Secretary Jim Mattis’ resignation letter, tendered in the wake of the president’s decision to pull U.S. troops out of Syria.

But Trump is even more incensed about news coverage indicating he needs adult supervision, Acosta told CNN’s Wolf Blitzer.

“He hates that letter,” Acosta said, citing a source close to the White House who “advises the president occasionally.” But he added that Trump is even more upset by the “conventional wisdom” that Mattis and some others in his administration “were sort of the adults in the room ... to keep the president from going overboard, to be a check on his impulses.”

Trump is “irritated by this notion here in Washington that he is sometimes in need of adult daycare,” Acosta added.

Mattis’ letter of resignation discusses his differences with Trump over several issues, one of them being the importance of strong international alliances, according to Mattis.

“While the US remains the indispensable nation in the free world, we cannot protect our interests or serve that role effectively without maintaining strong alliances and showing respect to those allies,” Mattis wrote.

Acosta spoke as members of the Senate were scrambling to come to some sort of compromise on a spending bill that would satisfy the president’s demand for funding for a border wall so the government wouldn’t be shut down. But both the Senate and House adjourned before a deal could be reached.

Acosta’s comments about Trump’s anger begin at the 3:30 mark in the video above.