Milley spoke to friends, lawmakers and colleagues about the threat of a coup, and the Joint Chiefs chairman felt he had to be "on guard" for what might come.
"They may try, but they're not going to f**king succeed," Milley told his deputies, according to the authors. "You can't do this without the military. You can't do this without the CIA and the FBI. We're the guys with the guns."
In the days leading up to January 6, Leonnig and Rucker write, Milley was worried about Trump's call to action. "Milley told his staff that he believed Trump was stoking unrest, possibly in hopes of an excuse to invoke the Insurrection Act and call out the military."
Milley viewed Trump as "the classic authoritarian leader with nothing to lose," the authors write, and he saw parallels between Adolf Hitler's rhetoric as a victim and savior and Trump's false claims of election fraud.
"This is a Reichstag moment," Milley told aides, according to the book. "The gospel of the Führer."