Muldoon was an exception. Somehow he found time to write, or dictate, a series of memoirs while running the country single-handed. Though I've not admitted it before, I enjoyed them immensely.
Brian Edwards did a book on Helen Clark in her second year of office which I reviewed too harshly. It was a work of unalloyed admiration and though it had some blind spots in my view, it gave insights to her upbringing, family and political life that were valuable. It is still on my reference shelf, dog-eared with stickers on useful pages and often borrowed by colleagues writing on her.
Key's life, up to the point of coming to power, was the subject of an excellent Herald investigation by former staff writers Eugene Bingham, Paula Oliver and Carroll du Chateau in 2008 and published by the paper in July that year.
Key had co-operated with the Herald's project entitled "The Unauthorised Biography" but I had no idea whether he would co-operate with mine.
Penguin Books were interested whether he co-operated or not, but I wasn't. It is possible to produce a book on someone's life using published records and the only willing sources, who are likely to be anonymous and antagonistic. That is not a book I wanted to write.
I didn't tell Key, so when I asked for his co-operation it was on the understanding he would not see the book before it was printed. He agreed, I gather, because he thought I would write it anyway.
My trepidation arose also from Penguin's need to put the book on sale well before the election campaign started, for a reason I well understood. Election campaigns are perilous for any political leader, no matter how popular they have been. Unexpected events can throw the best of them off balance, as "corngate" did for Clark in 2002 and "teagate" for Key in 2011.
Even if the campaign goes smoothly for them, there is no guarantee the winner will be returned to power under MMP. National could finish nearly 20 points clear of the next highest polling party but unless it has an absolute majority of the vote, Key could be history by Christmas.
Nevertheless, when the book goes on sale on Thursday, I am bound to be asked whether I think it will assist his re-election. The answer is in the latest opinion polls. National's support is at 50 per cent or higher in the latest round of polling in four different population samples.
Key's support could hardly be higher before anybody has seen the book. It will not be higher afterwards. Not even he entertains the possibility that National will win 50 per cent of the vote at the election. The campaign will be tough. David Cunliffe is no slouch. I admired his refusal to apologise for the Donghua Liu letter this week. He had no need to do so - forgetting a routine letter written 11 years ago and failing to find a record of it is perfectly understandable. His repeated denials that he had even known or helped Liu was forgiveable.
It was delicious irony after Cunliffe had made the most of Maurice Williamson's letter to the police on behalf of the same business immigrant and political donor, but no more than that.
Many a politician, including Key, would have apologised and got out of it. Not Cunliffe. It is rare in politics and public relations these days to see somebody stand his ground.
Key would look at it like the currency trader he was. When a trader finds himself in a losing position he exits quickly.
It is a principle Key believes more people should apply if they want to make money as he did.
The book is about more than politics, it is a life.
John Key, Portrait of a Prime Minister, will be published by Penguin Books on Thursday.
• John Key, Portrait of a Prime Minister, will be published by Penguin Books on Thursday.
