Heather du Plessis-Allan: Jacinda Ardern scores 6/10 in New York

COMMENT: It should've been a great week for the Prime Minister. She was always going to be in her element in New York. But really, it's hard to score her last seven days at any more than 6/10.

That score's not a reflection of what she did. Rather it's what she didn't do. And what was happening back at home.

What she did, she did extremely well.

Jacinda Ardern showed a deft sense of humour on the Late Show with Stephen Colbert. She showed nimbleness in dodging tricky questions from CNN's Christiane Amanpour. And she showed what an international star she is with every moment she spent in New York.

But none of that will take New Zealand voters by surprise. We know Ardern is charming, takes a good photo and gives a good interview. She's got the soft stuff nailed.

Also, she couldn't help that all the international media wanted to talk about was her being a mum.

But it meant Ardern had little room to do what she needed to for her own profile back home.

Which was to show her ability at the tougher stuff. She didn't do that.

Right now, Ardern needs to look tough. National is hitting her hard on being a weak leader. It's a vulnerability.

To be fair, a week at the UN doesn't really lend itself to her showing a harder side. Unless you're Donald Trump or Muammar Gaddafi, you're probably not going to use the UN's General Assembly to bollock someone. And few world leaders have enough time on the sidelines to really flesh out policy wins.

Mostly, a leader of a small country has to rely on speeches and face time with leaders of bigger countries to make a mark. Ardern had both and missed the opportunity.

Her highly-anticipated speech to the UN General Assembly was entirely forgettable but for the line "Me too must become We too".

Huh? What does that even mean? It doesn't make any sense. The whole point of the words "Me too" is to denote collective action, so expanding it to denote collective action is essentially a tautology.

If you're thinking about that, it means you're not thinking about the rest of the speech, so consider it a write off.

Another missed opportunity was the brief face time with Trump. Ardern bravely used it to press New Zealand's case for an exemption to the US' aluminium and steel tariffs. Good on her. We need an exemption. Australia already has one.

But, instead of really hammering to New Zealand voters how tough she'd been on Trump, Ardern recounted an amusing yarn about the moment being disrupted by someone knocking over a flag. Again, drowning out the hard stuff with soft stuff.

And it's what's happening back home that's really spoiled Ardern's week. New York was hardly the escape from domestic politics that it could have been.

The PM's own honesty is in the spotlight. Unfortunately, again. She's facing accusations she misled Parliament over the Derek Handley business.

The ins and outs of it are probably too beltway for most voters to care, but it's yet another cry of dishonesty aimed at the PM. Hot on the heels of accusations she was tricky with the truth in an interview about whether Curran's job was safe just hours before the announcement of Curran's resignation.

In neither case did the PM lie. It's just that she skirted around the full truth. Very easily. And that's enough to create questions of trust.

Which cuts to the integrity of a politician. And it's worse still when that politician has framed themselves as an anti-politician: able to deliver results without resorting to devious politics.

If that's the image the PM wants to project she has to be squeaky clean at all times. Disappointment is greater when voters expect more.

Ardern has to deliver. And not just on soft stuff.