On a Pacific cruise ship recently, passengers were subjected to a rant by an Australian ‘comedian’ – a word now synonymous with tiresome, left-wing prig – who made the mistake of assuming his predominantly Kiwi audience would respond positively to a sneering attack on Scott Morrison.

They didn’t, but he pressed on regardless. If only Jacinda Ardern could move to Canberra, he enthused. How great would that be? At which point someone in the crowd called out, to loud applause from the New Zealanders, ‘You can have her!’.

The interjection neatly encapsulated the predicament in which the New Zealand prime minister now finds herself: feted internationally, but struggling to get traction in the only place where it ultimately counts – at home.

When Ardern came to power in 2017 – not by popular vote, but due to the vagaries of New Zealand’s idiosyncratic electoral system – she cast a spell over the New Zealand commentariat. As the young leader of the Labour party, she was seen as heralding a generational change and an ideological reset in New Zealand politics. Internationally, she was acclaimed as a refreshing new leader in the same mould as Canada’s Justin Trudeau and France’s Emmanuel Macron.

The fact that she had a baby soon after taking office only served to enhance the aura around her. Even hard-nosed veteran press gallery hacks were smitten by baby fever.

A working mum who seemed effortlessly to balance parenthood with the demands of office, Ardern personified the ‘girls can do anything’ zeitgeist. Her stay-at-home partner, the affable TV fishing show host Clarke Gayford, completed what media commentators, many of them young and female, swooningly portrayed as a dream team.

Ardern’s international stocks rose even higher after her empathetic response to the Christchurch mosque massacres in March this year. Surfing a wave of international sympathy, she went to Paris to join Macron in launching the so-called Christchurch Call, a global initiative aimed at curbing the dissemination of online hate.

But while Ardern’s compassion for the 51 shooting victims and their families was undoubtedly sincere, it was no more than anyone should have expected from the prime minister of a country that prides itself on tolerance and inclusiveness. And doubts remain about whether the Christchurch Call, although similarly well-intentioned, will turn out to have been anything other than a well-timed public relations event.

Meanwhile, back at home, Ardern’s golden halo has lost much of its lustre. After a first year in power during which a doting media gave her an easy ride, her performance – and that of her ministers – has come under increasingly critical scrutiny.

Ardern’s cabinet is inexperienced, and it shows. Several of her government’s showpiece policies – most notably the Kiwibuild initiative, aimed at relieving New Zealand’s chronic housing shortage, and an over-ambitious forest-planting programme – have fallen spectacularly short of Labour’s promises.

Labour touted 2019 as its ‘year of delivery’ – a tacit acknowledgment that it hadn’t achieved much in its first year in power and had a lot of ground to make up. But the economy, buoyant under the former National party government, is stalling, and even in areas considered to be Labour priorities, such as the reduction of poverty and the number of people dependent on benefits, the government is making little or no headway

Once assured in the face of journalists’ questions, Ardern now often looks stressed. Her previously relaxed relationship with the media is starting to fray, as was evident on a visit to the remote Tokelau Islands in July when she was accused of trying to shut down awkward questions about a Maori land dispute near Auckland.

Her provocative statement at the more recent Pacific leaders’ forum in Tuvalu, when she said ‘Australia has to answer to the Pacific’ on climate change, indicated at the very least that she’s still a novice in international affairs. Even accepting the explanation that the statement wasn’t intended as a taunt or a rebuke, the ensuing furore was entirely predictable. It was the sort of gaffe the seasoned Helen Clark, New Zealand’s last Labour prime minister, would have been unlikely to make.

It didn’t look good, either, that Ardern’s main defender at the summit was the Fijian prime minister, Frank Bainimarama. It’s safe to say that most New Zealanders would rather have ScoMo as a mate than the Fijian strongman.

Ardern even has a sex scandal to contend with after a group of Labour party women complained of not being listened to when they made allegations of serious sexual assault against a male employee of the party. Questioned by journalists, she went to ground over the issue, insisting it was a ‘party matter’.

All this adds up to a perception that Ardern’s fairy dust, to quote one commentator, is wearing off. The most recent opinion poll showed her level of support as preferred prime minister had dropped from a peak of 51 per cent in April, immediately after the Christchurch terror attacks, to 41 per cent. The poll also showed Labour trailing National, although Ardern remains comfortably ahead as people’s choice for PM.

Trouble is brewing on her flank too, as her coalition partner and deputy prime minister, Winston Peters, increasingly goes off-script – as he did last week when he defended Australia’s right to burn coal, and earlier when he blindsided the government by demanding a referendum on abortion law reform. Peters’ poll ratings have plummeted since his party went into coalition with Labour and as the 2020 general election creeps closer, he can be expected to break ranks more frequently as he seeks to win back his socially conservative voter base.

So although Ardern still enjoys rock-star popularity abroad (she even features on the cover of the September issue of British Vogue, guest-edited by Meghan Markle), the reality at home isn’t so cosy. If it’s any comfort to her, there’s a precedent of sorts. In the 1980s, Labour prime minister David Lange bathed in the warm glow of international approval – from the left, anyway – for his impassioned opposition to nuclear weapons, but it didn’t stop his faction-ridden government disintegrating over economic policy. Lange eventually quit politics a bitter and disenchanted man.

On second thoughts, perhaps being reminded of that won’t be any comfort to Ardern at all.