John Key has moved to silence speculation he could quit in his third term if National looked like losing, after admitting he considered stepping down when things got tough in 2012.
Key has said he intends to serve a full third term, and yesterday said he would like to win a rare fourth term too, although that would be tough.
"I would like to, but in reality I've got to win a third term and the party has got to win a third term and elections are really difficult to win."
National had only once had a four-term government - in the 1960s under Sir Keith Holyoake.
"If we can get there it would be an amazing thing to achieve, but it's very difficult," Key said.
In a biography published yesterday, he admitted to "kicking the tyres" on quitting at the end of 2012 after a series of controversies.
They included his "Teagate" complaint to police about the recording of his conversation with John Banks, the pokies-for-convention centre deal with SkyCity, a U-turn over larger class sizes, the Crafar farms sale, assets sales and the Maori court challenge, Novopay, the Kim Dotcom raid and ACC's mass security breach.
He was worried about losing and had talked to his wife, Bronagh, about leaving.
"Losing feels like failure and I don't kinda like failure."
But Bronagh was pivotal in his decision to stay.
"Bronagh was much stronger on it than I was - that I would be running away, and why would I do that?"
Key said yesterday that in a strong marriage and in a job like his it was natural to ask your spouse, "are you fully committed to what's going on and do we believe this is the best thing for our family".
"Bronagh, as you can see from the book, was hugely supportive of me continuing as prime minister but we do this as a partnership together."
The biography, written by journalist John Roughan, catalogues the familiar story of Key's successful career as a currency trader, his upbringing in a Christchurch state house, marriage to Bronagh when he was 23, and his ambition from a young age to be a millionaire and prime minister - in that order.
It also discloses Key's blunt management style when in 2013 he sacked Phil Heatley and Kate Wilkinson "for nothing in particular they had done" because he wanted to refresh his Cabinet line-up.
At the time it was thought Heatley's earlier ministerial "time-out" for misuse of his ministerial credit card and Wilkinson's role as minister responsible for mine safety, in light of the Pike River disaster, were part of the mix.
The book was not authorised, although Key co-operated.
But he said he had nothing to do with the timing of the book's release and "no real authority" over it.
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