During the Republican primary, Marco Rubio was a common target. The plan was that Trump would praise Christie for defeating Rubio during a debate in New Hampshire.
Christie and Trump knew one another before the campaign through New York and New Jersey politics. They didn't attack one another as they did other candidates, CNN wrote in the book.
Christie lead Trump's transition team though the election until last week, when Vice President-elect Mike Pence took over the organization of the administration.
The book will be published Dec. 6, but can be pre-ordered now.