Labour's Maori campaign director Willie Jackson is not renowned for his humility, but even he probably didn't think he was this powerful.

Bemoaning the polls on Sunday, Jackson looked at then deputy leader Jacinda Ardern and joked "And it's all your fault Jacinda. They said you were going to change everything."

Two days later and they were indeed saying Ardern is going to change everything.

Labour MPs are fizzing at the bung in expectation.

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And it's a fair bet former Prime Minister John Key was on the blower to Bill English quick smart to advise him not to underestimate Ardern. He will have recognised something of himself in her.

While comparisons of Ardern and Helen Clark have been made, in style she is more like Key.

They are not politically similar, although Ardern describes herself as a pragmatic idealist, while Key was simply a pragmatist.

The similarity is in their ability to communicate.

Both are chameleons, able to adapt to different social settings and to talk to suit the audience they are addressing.

Both can use mass communication in a way that seems like personal communication - an invaluable skill in campaign debates.

Both manage to be very good politicians without looking like politicians.

English can sparkle when he needs to, but by and large he lacks the natural ability Key and Ardern have.

That might explain why National - which has fought three elections centred firmly on the Key factor - are now claiming elections are contests of ideas rather than personalities.

The tables are turned.

National will be revising its campaign plan - it might want to consider drafting Key in to help prepare English for the debates.

But National should not be the only ones worried about Ardern's impact.

The Green Party too might want to check its fences for holes. The first votes Ardern will attract will be those she gets back from the Greens.

Ardern's appeal is particularly high in urban areas - the very same areas the Greens have always polled strongest.

Ardern is the best revenge Labour could have served up for the Greens' recent behaviour.

Some might say the Greens only have themselves to blame for the rise of Ardern.

Many in Labour were furious with the Greens for milking Metiria Turei's confession for all it was worth, seemingly reckless of the damage it could do to the prospects of a Labour-led government.

It was that incident Little pointed to as the reason Labour slumped in the polls over that week.

True, it suited Labour to see those polls as a referendum on Turei's confession because that meant they were not a referendum on its own cornerstone policy - the families package issued the week before, in which it traded in National's tax cuts to upsize Working for Families, pump money into public services and introduce universal payments to parents of newborn babies.

It does not want those polls to be linked at all with that package, thank you.

But there was some anger as well over the Greens' unseemly and almost cruel gloating at the 1 News Colmar-Brunton poll in which they had rocketed up to 15 per cent.

Never mind that came at the expense of Labour and put Labour over the chasm of non-viability.

The Greens seemed oblivious to what Little openly admitted: that at those support levels, the much chanted "change of government" was not going to happen.

On paper and in the Greens' delusions MMP might deliver a government in which three similar-sized parties reign together, happily ever after. In practice, not on your nelly.

Ardern does not need to win votes off National, although she will take all comers.

All she needs to do is ensure the balance between Labour, the Greens and NZ First is more heavily tilted in Labour's favour.

That helps explain why Ardern has so far kept some distance from the Greens, delaying meeting the co-leaders and refusing to talk about Turei's admission of welfare fraud, saying she intends to stick firmly to Labour's campaign - not get drawn into '"distractions".

The other collateral damage in the change from Little to Ardern was to reporters who had already prepared election features on Little.

Among the items now sent to the recycling bin was a piece about a dog walk with Andrew Little and his twin sister Val.

That included the revelation of the naughtiest thing Little had ever done, according to Val. It was eating a whole can of sweetened condensed milk.

The leadership change has saved British Prime Minister Theresa May from losing top ranking in Great Sins of the Ages for running through a wheatfield.