A day ahead of the New Hampshire primary, Pete Buttigieg and Bernie Sanders remain on a collision course.

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The two candidates represent disparate wings of the Democratic party and are increasingly contesting frontrunner status in the contest for the nomination to face Donald Trump in November’s presidential election.

Buttigieg, a former mayor of South Bend, Indiana, identifies more as a centrist. Sanders, a senator from Vermont who sits as an independent, is a longtime favorite of the progressive grassroots of the party.

On Sunday, a Boston Globe/WBZ/Suffolk University poll found Sanders leading in New Hampshire with 26% support, followed by Buttigieg with 19% and the Minnesota senator Amy Klobuchar in third with 13%. It was the latest in a string of surveys showing Sanders or Buttigieg leading the rest of the field.

Iowa voted first in the primary, holding its caucuses last week. The outcome was muddled and both Buttigieg and Sanders have declared victory multiple times.

On the trail in New Hampshire, Sanders has repeatedly specified that he won the popular vote in Iowa by some “6,000” votes.

On Sunday night, the Iowa Democratic party released a new estimate of allocated delegates. It showed Buttigieg slightly ahead of Sanders.

Isaac Wright, a Democratic strategist who specializes in rural campaigns, said there was “absolutely” a rivalry between the 38-year-old former mayor and the 78-year-old senator.

“Mayor Pete has definitely shown a strong campaign and much like his other rivals, Bernie Sanders is taking shots at him,” Wright said.

Q&A What are the primaries? Show Hide The primaries and caucuses are a series of contests, in all 50 US states plus Washington DC and outlying territories, by which each party selects its presidential nominee. The goal for presidential candidates is to amass a majority of delegates, whose job it is to choose the nominee at the party’s national convention later in the year. In some states, delegates are awarded on a winner-take-all basis; other states split their delegates proportionally among top winners.

The two candidates are basically opposites.

Sanders’ signature issue in this primary is Medicare for All, an expansive proposal for healthcare reform. Buttigieg supports a slightly more modest plan he calls Medicare for All Who Want It.

Sanders has funded his campaign mostly with small-dollar donations. In addition to grassroots fundraising, Buttigieg has used traditional high-dollar closed-door fundraisers. Infamously, one such event, in California, was held in a posh wine cave.

“For two people in the same party, Buttigieg and Bernie are polar opposites in many ways,” said Monica Klein, a progressive Democratic strategist. “They represent the two wings of the Democratic party – which makes Buttigieg a great contrast candidate for Bernie.”

Facebook Twitter Pinterest Bernie Sanders supporters at a campaign rally in Keene, New Hampshire on Sunday. Photograph: Mike Segar/Reuters

In the last debate, on Friday in New Hampshire, Buttigieg and Sanders spent more time knocking other candidates, like Klobuchar or former vice-president Joe Biden, than each other.

Democrats expect that to change. In campaign stump speeches, the references to each other are there.

Q&A What are the New Hampshire primaries? Show Hide Most states hold primary elections, in which voters go to a polling place, mail in their ballots or otherwise vote remotely for a presidential nominee. These are much simpler than caucuses, which are hours-long meetings with multiple rounds of balloting. The first caucuses took place in Iowa on 3 February. Donald Trump won the Republican contest by a landslide, but the Democratic vote ended in chaos, with Bernie Sanders and Pete Buttigieg both emerging as winners in a contest that was too close to call.

New Hampshire traditionally hosts the first primaries of the election year and has done so since 1920. All eyes will be on the competitive Democratic primary to see which candidate comes out on top. There will also be a Republican primary, though as Trump faces no serious competition, he is expected to win that contest by a huge margin.

“This election is so vitally important because we need a true champion of the people in the White House who doesn’t kowtow to high money interest, that does not hold fundraisers in wine caves with Swarovski crystals,” the former Ohio state senator Nina Turner, one of Sanders’ campaign co-chairs, said at a rally in Claremont on Sunday.

Sanders has repeatedly bashed Buttigieg for how he raises money. At a recent event in Plymouth, he said “our views are different. Pete has raised campaign contributions from over 40 billionaires.” In Manchester on Monday, speaking pointedly, he said he did not “take money from the CEOs of pharmaceutical companies or from Wall Street goons … we don’t want their money, we don’t need them.”

Buttigieg has been slightly more opaque but his references to Sanders are still direct enough. And as he has toured New Hampshire, he has added a new line to his speech.

“I talk to a lot of people who tell me if their only choices are between a revolution and a status quo,” he said in Lebanon, “that doesn’t leave a lot of room for them.”

It was a clear references to calls by Sanders and his supporters for a “political revolution”.

Q&A Why is New Hampshire important? Show Hide While Iowa traditionally holds the first caucuses in the presidential election, New Hampshire has held the first primary since 1920. The goal for presidential candidates is to win early-voting states and create name recognition and a sense of momentum, as well to pick up their first delegates, who will eventually choose the nominee in summer. Sometimes a clear favorite for the nomination emerges quickly, but the last two major Democratic primary contests, pitting Barack Obama against Hillary Clinton and then Bernie Sanders against Clinton, have lasted from the Iowa caucuses in January through to late spring.

Buttigieg has also warned about the cost of Sanders’ plan for Medicare for All.

“What we could do without is a plan so expensive that Senator Sanders himself freely admits he has no idea how it’s supposed to be paid for,” he said recently in Dover.

To supporters, the rivalry is visible.

“I think there’s a lot of tension now between Pete supporters and Bernie supporters and Biden supporters,” said Colby Conner, a 20-year-old Dartmouth College student who went to see Buttigieg in Hanover on Saturday.

After Sanders’ Sunday rally, Lisa Matthews, from Lebanon, said her big priority was picking a candidate who could beat Trump. That seemed more like Sanders, she said.

“I feel like Bernie can get the young vote and young people don’t like Pete so much, from what I hear,” Matthews said. “I think Bernie can get the black vote and I’m worried that [Pete] has absolutely no visibility in the black community.

“So I think Bernie, overall, once we get farther along in the campaign, will do better than Pete.”

• This article was amended on 11 February 2020 to correct the age of Bernie Sanders from 79 to 78.