If you’re looking for a place to gauge the effect the ascendancy of Kamala Harris has had on the American presidential election, come to Carroll County, the only county in all of New England that arch-conservative Barry Goldwater carried as the Republican presidential nominee 60 years ago.

Here, and throughout the rest of New Hampshire, the electorate is especially sensitive to the political winds because of a heritage of more than a century of vital presidential primaries, and the Harris impact is vivid, telling, and potentially consequential.

Only weeks ago, this state – where the mountains stretch to the sky and the air is cool even when the rest of the country bakes – was considered in play for Donald Trump. Now, it seems to have settled back into the Democratic column.

Two months ago, when Joe Biden was still the presumptive Democratic nominee, the St. Anselm College Survey Center poll showed the President, who as recently as December held a 10-point edge over Mr. Trump in New Hampshire, running two percentage points behind. The latest poll shows Ms. Harris ahead by six points.

A similar movement is evident in the University of New Hampshire Survey Center poll, in which Mr. Biden held a tottering three-point lead in the state. Now, Ms. Harris holds a six-point lead over Mr. Trump in that poll – a phenomenon that, while not always as dramatic as it is in New Hampshire, is emerging in other states.

“For weeks, we were in despair here,” said David Van Note, a New Hampshire resident who has been active in national Democratic politics for decades. “Then all of a sudden Biden is out, Harris is in, and there is a feeling of great hope.”

That despair has deep roots. New Hampshire once was so Republican that the GOP prevailed there in 28 of the 34 presidential elections from 1856 to 1988, with Mr. Goldwater winning Carroll County in 1964 by 10 percentage points, though he lost the state to Lyndon Johnson.

In recent years, New Hampshire has been in full rebellion against the view of its most famous literary figure, Robert Frost, who in a poem published in 1920 – the year Republican presidential nominee Warren Harding carried the state in a landslide – wrote, “Yankees are what they always were.”

“This state was Republican, and reliably so,” said Ellen Fitzpatrick, a University of New Hampshire historian. “In the old days, New Hampshire and Vermont were the Republican counters to the Democratic dominance of Massachusetts. But that is a long-gone phenomenon.”

Recently, the Granite State has become more Democratic. The party has won here in seven of the past eight presidential elections.

New Hampshire veered into the GOP column in that period only in 2000, when George W. Bush took its four electoral votes largely because Green Party candidate Ralph Nader captured four per cent of the vote. Mr. Nader’s supporters would almost certainly otherwise have voted for vice-president Al Gore, delivering the state and the presidency to him, and making the spectacle of recounts in Florida meaningless.

Mr. Biden won New Hampshire by seven percentage points in 2020, the largest margin since Barack Obama (with Mr. Biden as his running mate) won the state in 2008.

Donald Trump took New Hampshire’s Republican primary in January, defeating Nikki Haley by 11 points. Ms. Haley, a former South Carolina governor, had calculated that the state’s voters were her best chance of stopping the former president’s march to his third presidential nomination. Her “NH for NH” buttons were everywhere, but the votes were for Mr. Trump.

That likely will not help Mr. Trump in November.

“Trump has a core here that he will get regardless, but he is not going to pick up any voters that already aren’t for him,” said Thomas Rath, a former state attorney-general who has been involved in Republican presidential politics for a half-century.

“Everything changed the day Biden got out. With Biden gone, Trump won’t pick up even three more people than he already has.”

This is a state that is, both figuratively and literally, independent.

Independents – voters not affiliated with any political party – count for 37 per cent of the vote, more than the figure registered by either the Democrats or the Republicans. The GOP holds a state-government trifecta: the governor’s chair and both chambers of the state legislature. But the Democrats control the state’s two seats in the U.S. Senate and its two seats in the House of Representatives.

Ms. Harris, who is Black and South Asian, may be able to shore up support among Black voters in states such as Georgia, who polls showed were less enthusiastic about Mr. Biden in this election than they had been in the past. But in New Hampshire, where Black, Indigenous and other racialized people make up only about 10 per cent of the population, a more important factor may be gender.

This state is comfortable with female leaders. Both of its senators, Maggie Hassan and Jeanne Shaheen, are women and so is one of its House members, Annie Kuster. As both parties will likely nominate women for the fall gubernatorial election, the next governor probably will be a woman as well.

“We are back to 2020,” said Andrew Smith, who runs the University of New Hampshire poll.

“Democrats lost their enthusiasm for Biden, and a lot of them felt they weren’t motivated enough even to show up to vote. Now, they have someone they feel they can vote for – and now we see it’s the Republicans who are losing their enthusiasm.”