Mr. Christie also describes some of the debate prep sessions that he led for Mr. Trump before he took the stage with President Joseph R. Biden Jr. last year. In one session, Mr. Trump turned to Mr. Christie and began to excoriate him for recommending Christopher Wray for F.B.I. director.

“He’s doing an awful job, and he’s your pick. He was your pick,” Mr. Trump told Mr. Christie in front of a half-dozen other Trump aides.

“Hold on a second,” Mr. Christie replied, praising Mr. Wray. “He wasn’t my pick. He was your pick. He was my recommendation. I’m not the president. I don’t get to pick.”

Mr. Christie reveals how worried he and others were for his survival when he became infected with the coronavirus after being at the White House around the same time that Mr. Trump and several other aides contracted Covid-19. Mr. Christie writes that his priest arrived in the hospital and rubbed oils on his forehead in the sign of the cross, praying over him.

He got a call from a hospitalized Mr. Trump, who had one main concern: “Are you gonna say you got it from me?” Mr. Trump asked him.