Emails between Mr Slater and Mr Lusk appear to show they wanted him to win, and discussed payments from him; Mr Mitchell has emphatically denied ever paying either of them.
Whale Oil attacked Mr Robinson for his "cult" religious beliefs that could poison the party, and accused him of stacking the branch with members of his local church.
Blog posts then turned on candidate Scott Simpson, calling him "negative", "too old", and "not particularly likeable". Mr Simpson eventually left to stand in, and win, the Coromandel seat. Mr Robinson said the accusations were "absolute rubbish".
"I go to a small church on the Hibiscus Coast. If 150 people that go to church can dominate New Zealand politics, then New Zealand politics must be a very small boat. I was encouraged to find members. I did that, other candidates did that.
"Things that were said were pretty atrocious ... To have that sort of stuff written about you, to have reporters turn up at my children's school and outside my office from stories that were deliberately leaked as part of the smear campaign, it was very upsetting for all of us."
He was considering legal action - though as a last resort.
"It was my character and reputation that was targeted ... There's no upside in this for me, and probably no upside for the National Party. But the fact is that it took place, and there's no place for it."
Mr Robinson said he approached Mr Lusk in 2011 for help with speech writing, but was turned down because Mr Lusk was working for a rival.
Mr Mitchell said Mr Lusk had given him guidance on speeches and brochures.
"He was never working for me, he's never had an official role with me." Mr Lusk could not be reached for comment.
Mr Mitchell said the narrative in Dirty Politics was completely false, and he was considering legal action.
Jennie Georgetti, Rodney branch deputy chairwoman at the time, said the selection was fair and robust, and it was far-fetched to suggest Whale Oil had had an influence. Mr Slater said via email: "Everything I wrote was true and to cap it off it is up to the delegates in Rodney to choose."
Asked to comment on emails that suggest he was paid by Mr Mitchell and pushing for him to win, he said: "Don't care what Nick Hager has published out of context. Never received a cent from Mark Mitchell."
Meanwhile a row has erupted between the deputy chairs at the time.
Jennie Georgetti said the process was robust and fair, but her fellow deputy chair at the time, Glenys Ferguson, disputes this.
"Believe me it was not fair and it was not robust. It was a conspiracy, the nastiest behaviour I've seen. It was a nightmare," said Mrs Ferguson, whose favoured candidate Brent Robinson was the subject of heavy criticism from Whale Oil.
She said several committee members, including herself, the chair and the secretary, quit in the aftermath in protest.
She also quit her position as chair of the Whangaparaoa branch, though she remains a member of the National Party.
"I was not bitter, more sickened than anything else. I refused to be elected chair after that."
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