Secret diplomatic cables describe a frustrated country filled with testosterone-fuelled working-class men clamouring for a new populist leader.

It's not the United States in 2016, but New Zealand, 1975.

Cables from the US embassy in Wellington, revealed by WikiLeaks, offer colourful perceptions of Kiwis, their forceful new leader Robert Muldoon, and the anti-nuclear debate.

One cable nine months before polling day confidently predicted Muldoon would win the 1975 election. Classified "secret", it showed Muldoon already gave an "assurance" to back nuclear-powered warship (NPW) visits and would corral his ministers to approve a pro-nuclear policy.

The following year, a lurid cable dissected the national psyche, and explained Muldoon's appeal.

"In a country which very highly values amiability and polite civility, Muldoon's weakness for the rude retort gets him in trouble with some New Zealanders."

It said blue-collar workers "full of resentments, hungry for excitement and looking for ways to let off steam" fuelled Muldoon's victory.

It said he bonded with rough-and-ready voters who engaged in a widespread pastime called the "Saturday night massacre".

US diplomats described that as "a sodden beer orgy in which boozers smash each other with fists and bottles and subsequently smash each other with automobiles".

Muldoon's combination of "unimpressive physique and powerful mind could explain his conditioned reflex of hurling well-aimed verbal counter bolts when he sees himself challenged", the writer added.

The cables include much unreported content and come from leaks, documents released under Freedom of Information laws, and US State Department declassification reviews.

Jim Bolger, prime minister from 1990-97, disagrees with the cables' characterisation of Muldoon voters and says the so-called "Rob's Mob" was never properly described.

Some of them described Muldoon's rough exterior as masking a "sensitive" inner world, mentioning his lily cultivation habit.

But one urged acquiescence with Muldoon's advice about getting nuclear-powered cruiser USS Truxtun to visit New Zealand.

"I strongly recommend that we continue to be as cooperative and helpful as possible to (this) highly pro-American present government," a diplomat wrote in July 1976 to recipients including secretary of state Henry Kissinger.

Americans believed Muldoon was perhaps pig-headed enough to disregard, or at least overcome, public opinion about nuclear-powered warships.

Muldoon indicated a "substantial sector of public opinion" opposed his decision to allow NPW visits but that would not deter him.

US predictions weren't always spot-on. In 1976, one suggested bilateral "irritations" over the NPW ban were likely to "disappear".

Former prime minister Jim Bolger, a minister in Muldoon's government, said "the general mood was pro-American on defence alliance issues" during the time in question.

The cable's reference to Saturday night massacres was "a gross characterisation" and simplification of mid-70s New Zealand, and of Muldoon voters.

"I never had any involvement in Saturday night massacres at all. I think it's some colourful pen at the US embassy."

He said Muldoon's cabinet included many World War II veterans, who viewed the alliance with America favourably, as Muldoon did.

"He was a robust product of his era, and that included World War II.

"He was a formidable politician, no question about that, and he was a very robust debater."

- Stuff