I blame the children. If there were family reasons for John Key's decision to stand down, they were surely the demands of his art-school daughter or YouTube son: Dad, enough with the stability meme, if you want to be on-fleek in world-gone-mad 2016 you got to burn it down, chuck it in.

And so the Prime Minister - the most popular, it seems uncontroversial to say, in New Zealand history, certainly the most consistently underestimated - has chucked it in. Notwithstanding the magical thinking of his deepest enemies, who have conjured every imaginable conspiratorial explanation (may I at this point politely suggest he's definitely joining the Trump cabinet, alongside the likes of "Mad Dog" Matthias), Key has done it on his terms, at his own time of choosing.

Last week, John Key celebrated a decade as leader of the National Party. They said he'd been PM for eight of those. That seemed impossible - hadn't he been running the shop for longer than that? When wasn't he prime minister? I swear I remember him celebrating the 1987 World Cup win. He was definitely there at Sesqui. I'm pretty sure there are photographs of him on the pink and white terraces. The Forrest Gump of New Zealand politics.

And nothing became him like the leaving: there was no hum of speculation, no whispery gossip. Key's grip on power was so inviolable that Paula Bennett and Judith Collins could last week post pictures of themselves made up in costume for a pirate-themed party, and no one even thought to crack a plank-based Key gag. Somehow, he had inoculated his squad from the ravages of third-termitis.

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By setting out a seven-day timetable, Key has forestalled much potential for splintering within caucus; by endorsing his deputy, Bill English, he delivers all but a coronation.

English's strange reluctance to immediately commit to standing left a door open for Judith Collins to air her ambitions, but it seems unavoidable that English will lead National for a second time round. For how long, though? Any new leader will have to give serious thought to an early election: we're going to the people in March, to deliver a mandate to the new PM!

The risk for the party now is that the dam bursts: that the perturbations within caucus, made invisible by loyalty to an unalloyed winner, become the story. And the only thing more amazing than the fact we'll have a new prime minister this time next week is that the party most under scrutiny for its leader in next year's election will not be Labour.