National Leader Simon Bridges is engaging in his war of words with psychologist and TV personality Nigel Latta, accusing him of masquerading as objective when he's actually "deep on the left".
In response, Latta told the Herald he was "surprised and disappointed" that the leader of the Opposition was resorting to personal slights.
He said it would be better for the quality of New Zealand's political conversations if Bridges focused on the issues, rather "personal attacks" on people who challenge him.
"That's a style of politics we've seen overseas. I don't think we need it here."
The pair had been exchanging blows on Twitter for a few days, after Latta accused National of "embracing Trump's approach to the truth" over its criticism of the Government's forecast deficit.
Last week, Treasury revealed it expected the Government to go into deficit in the current financial year, which ends June 30, 2020.
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But it also forecast that the Government would run surpluses over the next four years, totalling $12 billion, despite the $1b deficit.
National has been highly critical of the forecast.
In a social media post, the party said the Government has been "experimenting with your money and you'll pay for the consequences".
It was with this post that Latta first took issue.
"Just because this stuff works for Trump doesn't mean you should do it too," Latta said in response to the post.
"Our political conversation should be better than this. We are better than this."
In another tweet, Latta doubled down and said that under the previous National government there was a housing crisis and "crumbling health infrastructure".
"I just don't want to live in the NZ that Simon Bridges and National want to create. Instead, I believe in a NZ where all of us matter, not just some of us."
The back-and-forth between the pair continued online for a few days until Bridges was asked about the feud this morning at Parliament.
"He's a guy who trades as an independent boffin who's kind of nice and straight down the middle – the reality is he is clearly deep on the left; he doesn't like National," he told reporters.
Bridges said that Latta was entitled to his opinion, but he should not "dress it up with some sort of pseudo-science objectivity".
He added that drawing attention to the forecast deficit next year was important, as it showed the Government was mismanaging the books.
"New Zealand was looking at surpluses as far as the eye could see; the Government has mismanaged that into deficit."
But Westpac Senior Economist Michael Gordon said one projected deficit was really not a big issue.
"It would be more of an issue if there were forecasts of ongoing deficits – but a single deficit is not an issue in itself."