United States President-elect Donald trump had told New Jersey Governor Chris Christie in 2015 that he didn't expect to make it past October, reveals an upcoming book by CNN on the 2016 Presidential elections.

Christie's endorsement of Trump had shocked observers in February this year as the first sign of capitulation from the Republican establishment to the man who would eventually become their nominee -- and then their president.

However, it could've easily been the other way around, according to the book Unprecedented: The Election that Changed Everything, written by CNNs Thomas Lake with reporting from Jodi Enda, Susan Baer and CNNs political team.

'Trump told Christie in 2015 that he didn't expect to make it past Octoberat which point he would endorse Christie, according to a Christie adviser who asked not to be named in order to speak about behind-the-scenes maneuvers,' the book says.

'I think they always had an understanding that the first one out would probably endorse the other,' the adviser had said.

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