"The events of the last couple weeks have caused me to do deep soul-searching, and I can no longer faithfully support and execute your orders as Chairman of the Joint Chiefs of Staff," Milley wrote in the draft letter obtained by Glasser and Baker.
"I believe that you have made a concerted effort over time to politicize the United States military," he continued.
"I thought that I could change that. I’ve come to the realization that I cannot, and I need to step aside and let someone else try to do that."
The big picture: Milley also feared that Trump was seeking to use the military to remain in power.
"You are using the military to create fear in the minds of the people — and we are trying to protect the American people," Milley wrote in the letter dated June 8.
"The American people trust their military and they trust us to protect them against all enemies, foreign and domestic, and our military will do just that. We will not turn our back on the American people."
State of play: Milley in the end decided to stay. "F---k that shit," Milley told his staff, per the New Yorker. "I'll just fight him."
Milley sought to prevent Trump from doing any more damage, while also carrying out his obligation to respond to the orders of his commander in chief, according to the magazine.
"If they want to court-martial me, or put me in prison, have at it," Milley told his staff. "But I will fight from the inside."
Between the lines: The excerpt also details how Trump grew increasingly frustrated by his national security officials and wanted more loyalty from them.
"You f*cking generals, why can't you be like the German generals?" Trump complained one day to former chief of staff John Kelly, per the New Yorker.
"Which generals?" Kelly asked.
"The German generals in World War II," Trump responded.
"You do know that they tried to kill Hitler three times and almost pulled it off?" Kelly said.
"No, no, no, they were totally loyal to him," Trump replied.