Jacinda Arden's elevation as Labour leader has sent a chill through the National Party in inverse proportion to the sheer radiance emanating from the Labour caucus over the change.

If National was complacent about Ardern before her acceptance press conference, it certainly wasn't afterwards. They could see the threat for themselves.

Its attacks on Labour which proved so effective when Andrew Little was the target simply won't stick.

It is harder to portray Labour as relentlessly negative with Ardern and her relentlessly positive beaming smile taking up half the screen.

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It is hard to portray Labour as a party in disarray when it has just elected a young new leader unanimously.

National could play the experience card but even that is likely to rebound.

Ardern was just 10 years old when Bill English was first elected to Parliament. And while she has not been a minister or part of the leadership group for long, she has been in Parliament far longer than John Key had been when he was elected. He became Prime Minister with no ministerial experience.

Ardern's press conference was a command performance of a competent new leader that stunned most of those watching, and especially those who believed she was not a woman of substance.

She is not the first Labour or National leader to have given a magnificent debut press conference.

Bill English did in December when he became Prime Minister. And David Cunliffe did when he won the Labour leadership in 2013.

The difference is that English's shine has worn thin. Ardern is not naturally dull and does not have to try as hard to keep voters' attention.

And the leadership change has been so close to the election that there will not be time for Labour's splits and divisions to re-emerge as they did after the mid-term change to Cunliffe.

Ardern does not have to become Labour's Joan of Arc to succeed. Those expecting her to be the party's salvation and deliver them the Government benches in eight weeks' time have set their expectations too high.

One thing that is not likely change is the influence of Winston Peters and New Zealand First over the result of the election even if Ardern turns around Labour's fortunes.

Her task is to save Labour from a humiliating dive in the polls. Even maintaining its current position would be success of a kind. If she gets it heading north again, she will be a legend.