Milley, who was chair under Trump and President Biden, also fears he would be court-martialed should Trump win the presidency next month because the commander in chief has power over retired commissioned officers and can recall them to active duty and court-martial them.

Such a situation is not out of the realm of possibility because Trump has often voiced his desire to take revenge on those who have spoken out against him.

"He is a walking, talking advertisement of what he's going to try to do," Milley warned former colleagues, according to Woodward. "He's saying it and it's not just him, it's the people around him."

Woodward cites Steve Bannon, a former senior Trump adviser, who earlier this year gave a list of people he believes Trump should go after if he is elected to a second term, including Milley, former FBI directors Andrew McCabe and James Comey, former Secretary of Defense Mark Esper and former Attorney General Bill Barr.

"We're gonna hold him accountable," Bannon says of Milley in the book.

Bannon is in jail for contempt of Congress.