John Armstrong: Decision a blow for National

National's Simon Power has announced he is leaving Parliament to pursue new challenges and new opportunities. Photo / Sarah Ivey

And the next leader of the National Party is ... well, step up to the mark, Steven Joyce. If John Key stepped down tomorrow, the only other viable candidate just ruled himself out.

Simon Power's decision to quit left Mr Key "stunned and flabbergasted". He is not the only one.

Politicians normally stick around long past their use-by date. As for walking away from it all at the zenith of one's power (sorry) and influence, well, forget it.

In the space of barely three months, however, two senior ministers have done just that, the other being Defence Minister Wayne Mapp.

Mapp's move is understandable. He is 59 this month, and unlikely to get any higher up National's pecking order. Power's decision is harder to fathom.

Assuming National wins the forthcoming election, National's fourth-ranked MP would have basically been given any portfolio he wanted in the subsequent Cabinet reshuffle.

His departure is a major loss for National. Articulate, competent and fastidious to a fault, Power is also blessed with a high degree of common sense - a commodity which tends to evaporate once someone is in the Beehive.

He was touted as a future leader. But while National has been odds-on to win this year's election, 2014 will be more difficult. If National lost, it would mean Opposition again, possibly for two terms.

As leader, that would mean it would be 2020 before Power got the keys to Premier House.

In the interim, there would always be the possibility that someone might leapfrog him.

Power poo-poos such supposition, saying politics is winning the battle of ideas, not a beauty contest - a view which was reinforced just prior to National becoming the Government by Winston Peters' appearances before the privileges committee, which Power chaired.

When it comes to explaining why he is quitting, Power has to be taken at his word. But that will not eradicate the nagging feeling that there must be other reasons why someone who even yesterday was saying politics flowed through his veins like blood is not staying for the long haul.

Then again, 12 years in Parliament may be long enough.