Heather du Plessis-Allan: It's fair to compare Jacinda Ardern to Donald Trump

Jacinda Ardern is more like Donald Trump than she would like to think.

The comparison was first made by the Wall Street Journal just before last year's election. In a tweet, the WSJ said: "Meet New Zealand's Justin Trudeau - except she's more like Trump on immigration."

This week, Ardern told the US-based NBC's Today Show that the comparison "infuriated" her.

She may have to suck it up because the comparison is fair. And it goes beyond just immigration.

Both Trump and the Labour Party campaigned on drastically reducing immigrant numbers. Ardern may try to wiggle out of that by pointing out that Labour campaigned to double the refugee quota, but that's just nice PR. The refugee policy was a footnote in the immigration debate where Labour promised to cut immigrant numbers by 20-30,000. Labour's main message was anti-immigrant. So was Trump's.

So how does the comparison go further? Both Trump and Ardern have been put into power by a minority of voters. Trump took 46 per cent of votes, against Hillary Clinton's 48 per cent. Ardern took 37 per cent of the vote, against Bill English's 44 per cent.

Yup, Labour supporters say the election was won fair and square. And it was. That's how the system works. Trump supporters say exactly the same thing.

And there's another comparison. Trump's and Ardern's elevations to power are aggravating a big group of voters in their respective countries. Voters on the losing team aren't dealing well with the election of the underdog.

Take a look at this week's TVNZ political poll.

It's astounding that National's voters refuse to abandon it. There they sit at 44 per cent. That's exactly the same support the Nats got at the election seven months ago. By now, you'd expect them to be jumping ship from the election losers.

Compare that to what happened after the last change of government. Labour lost power in November 2008. Within three months, its voters had started leaving. By February, its polling had slid from 34 per cent to the mid-20s.

There's a good chance those National voters are refusing to budge because they're still angry at the sense the election was stolen. Because they're angry and vocal in their criticism, supporters of the Government have become more defensive and protective of the Prime Minister.

And so left and right voters end up fighting about subjects as esoteric as oil and gas. Did you ever expect the Government's oil and gas decision to blow up in the way it did?

Most punters don't really care about oil and gas. It's not something that's kept them awake at night. They don't even necessarily know much about it. You can tell that by some of the pretty dodgy facts being bandied about.

But the decision is symbolic. It would never have happened under National. So National voters see it as reckless disregard of the economy. Left-leaning voters see it as a huge win and evidence of the Government's commitment to caring for future generations. There's no in-between.

I can't help but think that this is a sign our country is divided in a way it hasn't been for decades. We're not yet as divided as the 1980s, but we're heading that way. Back then you either loved or hated Muldoon, the nuclear-free issue, the Springbok Tour, the reforms of the Fourth Labour Government.

New Zealand's deepening divisions are not unique. It's possible we're just catching up with the wave of division we've seen sweeping the world in recent years. From the generational battle of Brexit, through to the educational/racial/wealth/geographical/God-knows-what-else-is-causing-it battle that led to Trump's election in the US.

So there. Comparing Ardern to Trump isn't that far off the truth.

• Heather du Plessis-Allan is on NewstalkZB Wellington, weekday mornings.