Every day is important in the election campaign but today will be Jacinda Ardern's most important yet.

TV1's debate tonight, hosted by Mike Hosking, will give the public its first chance to compare the new Labour leader with Prime Minister Bill English, side by side.

An hour before it starts at 7pm, the results of the latest Colmar Brunton poll will tell her whether the surge in support for Labour has continued, slowed or stopped.

She had a flawless campaign launch in Auckland 11 days ago, but English and National have had a relatively strong week since their own launch on Sunday, despite accusations of dirty politics by Winston Peters.

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His accusations lost a bit of their punch when he made it clear he could still be open to forming a Government with the very people he more or less called dirty rotten bastards.

In some ways Ardern's job will be simpler than English's in the debate.

The expectations of a knock-out performance by her will be low, given she has been leader for just over four weeks. She will be considered a success if she comes away looking half-way competent and able to foot it with English. She has an advantage over him in that the camera loves her and she is instantly likeable.

That assists her in sound-bites and television news clips on the news but tonight's hour-long format will be less forgiving. She is vulnerable on the economy. She can't possibly have the depth of experience and knowledge that English has had as Finance Minister for eight years.

She is especially vulnerable on the number of new taxes Labour definitely would and probably would introduce, to such an extent that the last tax -- $25 on foreign tourists -- was announced by a spokesman.

Viewers will be looking for substance, not platitudes. They will not be looking for technical victories. They will not be looking for which leader has the best memory for figures and reciting facts.

The winner will be the leader who is genuine, who makes connections to their own lives, although as Metiria Turei's example showed, there are right and wrong ways to make connections with people.