Defense Secretary Jim Mattis reportedly refused to implement an order from President Donald Trump that would have caused the death of “the f*cking lot” of Syrian government employees — including President Bashar Al-Assad, according to veteran reporter Robert Woodward.

The Washington Post reported on Tuesday that Woodward’s new book, “Fear: Trump in the White House,” details Trump’s reaction to the use of chemical weapons in Syria.

With Trump’s rage and defiance impossible to contain, Cabinet members and other senior officials learned to act discreetly. Woodward describes an alliance among Trump’s traditionalists — including Mattis and Gary Cohn, the president’s former top economic adviser — to stymie what they considered dangerous acts.

“It felt like we were walking along the edge of the cliff perpetually,” Porter is quoted as saying. “Other times, we would fall over the edge, and an action would be taken.”

After Syrian leader Bashar al-Assad launched a chemical attack on civilians in April 2017, Trump called Mattis and said he wanted to assassinate the dictator. “Let’s fucking kill him! Let’s go in. Let’s kill the fucking lot of them,” Trump said, according to Woodward.

Woodward revealed that Mattis refused to follow Trump’s order to the letter.

“We’re not going to do any of that,” Mattis reportedly told an aide. “We’re going to be much more measured.”

Trump eventually agreed to a plan for a limited conventional airstrike on a Syrian airfield.

Woodward also described a “nervous breakdown” within the White House that caused top aides to hide documents from the president’s desk.

“We’re doing this in order to prevent World War III,” Mattis told Trump after he was asked why the U.S. is spending money to detect North Korea missile launches.

Read more about Woodward’s book here.