Gen. Mark Milley, the chairman of the Joint Chiefs of Staff, drafted a letter of resignation in June 2020 following former President Donald Trump’s infamous photo-op in front of a torched church near the White House — before changing his mind and vowing to oppose the 45th president “from the inside,” according to a forthcoming book.

In the draft, Milley accused Trump of using the military to “create fear in the minds of the people” and alleged the then-president was making “a concerted effort over time to politicize the United States military.

“I thought that I could change that,” the general went on. “I’ve come to the realization that I cannot, and I need to step aside and let someone else try to do that.”

The letter was reprinted by the New Yorker Monday as part of an excerpt from “The Divider,” the forthcoming tell-all from the husband-and-wife reporting team of Peter Baker and Susan Glasser.

According to the authors, Milley considered stepping down after receiving criticism for accompanying Trump part of the way across Lafayette Square after it had been cleared of Black Lives Matter protesters on June 1, 2020.

“As they walked, with the scent of tear gas still in the air, Milley realized that he should not be there and made his exit, quietly peeling off to his waiting black Chevy Suburban. But the damage was done,” write Baker and Glasser, who note that Milley had been pictured walking a few steps behind Trump while clad in combat fatigues, “an image that seemed to signal that the United States under Trump was, finally, a nation at war with itself.”

Eventually, Milley opted to stay on after consulting several elected and military officials — including his predecessor as Joint Chiefs chairman, Joseph Dunford, and former Defense Secretary Robert Gates — who reportedly told both Milley and Defense Secretary Mark Esper: “If you resign, it’s a one-day story. If you’re fired, it makes it clear you were standing up for the right thing.”

Baker and Glasser write that both Milley and Esper, as well as then-Attorney General Bill Barr, had resisted Trump’s demands to invoke the Insurrection Act of 1807 and send in 10,000 active-duty troops to crush the DC protest that had mushroomed after the murder of George Floyd by Minneapolis Police officer Derek Chauvin.

“We look weak,” said Trump, who reportedly raged that his advisers were “f—ing losers” and purportedly asked Milley: “Can’t you just shoot them? Just shoot them in the legs or something?” 

Milley later issued a public apology for his appearance at Lafayette Square, saying during his June 11, 2020 commencement address at National Defense University: “I should not have been there. My presence in that moment and in that environment created a perception of the military involved in domestic politics. As a commissioned uniformed officer, it was a mistake that I have learned from, and I sincerely hope we all can learn from it.”

In private, Baker and Glasser write, Milley had told his staff of Trump: “F— it, I’ll just fight him.”

“If they want to court-martial me, or put me in prison, have at it,” Milley reportedly added. “But I will fight from the inside.”

The excerpt contends that Trump had a fractious relationship with the Pentagon, from whom he reportedly expected unswerving loyalty.

“You f—ing generals, why can’t you be like the German generals?” Trump told then-White House Chief of Staff John Kelly at one point, according to Baker and Glasser.

“Which generals?” Kelly asked.

“The German generals in World War II,” Trump reportedly responded.

When Kelly told Trump that Hitler’s generals had tried to kill him on three separate occasions, the president brushed it off, saying: “No, no, no, they were totally loyal to him.” 

“The Divider” – set to come out Sept. 20 – also features Milley’s recollection of a conversation Trump had with then-acting Defense Secretary Christopher Miller three days before last year’s Capitol riot. 

In the excerpt released Monday, Milley reportedly heard Trump tell Miller that the “Stop The Steal” rally planned for Jan. 6 was “going to be a big deal.”

“You’ve got enough people to make sure it’s safe for my people right?” Trump then asked, to which Miller responded that he did. According to the authors, Milley never saw Trump in person again.