WHEN Jacinda Ardern was elected deputy leader of the Labour Party in March, she was unknown to most New Zealanders. The soft-left party was favoured by less than a quarter of voters when her uninspiring boss, Andrew Little, resigned last month, thrusting her into what she described as “the worst job in politics”. The change was akin to “anointing a prophet”, notes Raymond Miller, a professor at the University of Auckland. Labour has staged an unprecedented resurgence, climbing by as much as 20 points in some polls. That has cast doubt on the outcome of an election on September 23rd which had previously seemed certain to provide the right-of-centre National Party with another term in government.

The local press calls it “Jacindamania”. At the tender age of 37, Ms Ardern has harnessed what she calls a “mood for change”. Not all locals have benefited from the strength of New Zealand’s economy. Wages are stagnant and the price of housing has soared, feeding a debate about New Zealand’s high levels of immigration. A record 71,000 more people arrived in New Zealand last year than left, partly because Kiwis who had left the country have been lured home by a stronger economy. Inadequate investment in housing has exacerbated the problem: New Zealand needs 60,000 new homes. The government spends NZ$140,000 ($100,000) a day accommodating the homeless.

Unusually for a left-leaning leader, Ms Ardern has put immigration at the heart of her campaign, proposing to cut net arrivals by up to 30,000 annually. Labour also plans to ban non-resident foreigners from buying homes, arguing that it is wrong that American tech billionaires and Chinese investors can snap up houses and leave them empty amid such a shortage. (The Nationals, in contrast, say curbing immigration would hurt the economy.)

But Ms Ardern rejects the idea that she is trying to stir up or harness hostility towards immigrants. If the government had responded faster to the housing crisis, she says, “we would not be having this conversation.” Labour also wants to double New Zealand’s intake of refugees. Her real target, she says, is the high cost of living: “I want everyone who chooses to call New Zealand home to have a decent start.” To that end, she also promised to abolish tuition fees for university students.

Yet personality, as much as policy, has underscored Labour’s resurgence. Her sudden ascendancy has left Ms Ardern with “no time to be anyone other than me”, and many voters are enthralled. Critics point to her youth and relative inexperience: she has been a member of parliament for nine years, but only in opposition. Yet others see energy and a breath of fresh air. Those who have worked with her say she is dedicated and considerate. Her campaign has been characterised by a rare brand of what she calls “relentless positivity”. Posters of her beaming face are emblazoned with the slogan: “Let’s do this!”

In charm and charisma, Mr English, who took over the top job when his predecessor resigned last year, is eclipsed. During a previous stint as leader of the Nationals in 2002, he presided over a crippling defeat. Yet he has a reputation for credibility. During his eight years as finance minister unemployment fell, the budget returned to a surplus and New Zealand enjoyed one of the highest growth rates in the rich world. Ms Ardern, by contrast, has never championed a weighty bill or served as a minister. Some of her crowd-pleasing goals, like eradicating child poverty, seem unlikely to be met. In other areas she is accused of being uncomfortably vague. “You can’t replace a tunnel with a vision,” the prime minister scolded her during a debate about infrastructure.

In the face of this unexpected opposition, Mr English has made late promises to increase spending on roads and housing. He is favoured by farmers who have thrived on Chinese demand for New Zealand’s milk. Kiwis may ultimately plump for his tried-and-tested approach. That would make the election memorable for stability, rather than a shake-up: another victory would give the Nationals the longest stint in government for any party in almost 50 years.