The results also indicate how the wider public perceive Mr Hager. Eleven per cent said it would do a lot of damage because Mr Hager did not make things up, while 14 per cent thought being attacked by Mr Hager - who National has dubbed a conspiracy theorist - would actually enhance Mr Key's standing.
National has centred its campaign on Brand Key to take advantage of his reputation and popularity.
Jennifer Lees-Marshment, a political communications expert at Auckland University, said the biggest concern for Mr Key was that all the attention on the book was making it hard for him to convey National's "vision" for the next three years. That made this weekend's campaign launch critical for him.
However, she said Mr Key did have a very strong, longstanding brand to pit against the book.
But she said there were risks. "All of this muck-raking, and particularly the negativity of it, may make people start to doubt" their perception of his leadership.
By Claire Trevett