Open this photo in gallery A volunteer with Democratic presidential candidate Sen. Bernie Sanders hands out signs before the start of a rally in Boston, on Feb. 29, 2020. Mary Schwalm/The Associated Press

Emmanuel Masson was a long way from his Ottawa home as he approached a blue clapboard bungalow in a leafy suburb of Charleston, S.C., one day last week.

The homeowner, a 53-year-old high-school teacher named Carl Calvert, greeted him in the driveway. Mr. Masson, a lanky 22-year-old with a shock of dirty blond hair, introduced himself as a canvasser for Bernie Sanders and struck up a conversation.

When Mr. Calvert mentioned his medical bills – US$37,000 after an exploding gas can left him with serious burns to his legs – Mr. Masson saw his opening.

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“Have you heard about Bernie’s Medicare-for-all plan?” he asked.

Mr. Calvert was impressed by the outreach.

“I’ve lived in this neighbourhood for 22 years and you’re the first person I’ve seen here with a political campaign,” he said.

People such as Mr. Masson are a ubiquitous presence on the campaign trail during the Democratic presidential primaries: enthusiastic volunteers for Mr. Sanders willing to journey across the country and, in some cases, over international borders to flood into key states. Unpaid and travelling on their own dime, they sometimes spend weeks away from home rallying support for the man promising revolutionary change in the United States.

These foot soldiers have helped vault the Vermont Senator into front-runner status. While Mr. Sanders came up short in South Carolina, finishing second to Joe Biden, he has won the most votes in all three of the other early-voting states. On Tuesday, his volunteer army will face its greatest test so far. Fourteen states will vote simultaneously, including delegate-rich California, where Mr. Sanders currently leads the polls.

On Sunday, organizers put out a call for 300 volunteers to help out at a rally for Mr. Sanders in San Jose. So many more than that showed up that the campaign had to turn people away.

Open this photo in gallery Presidential candidate Sen. Bernie Sanders holds a campaign rally at the Los Angeles Convention Center, on March 1, 2020. David McNew/Getty Images

“The numbers are just staggering. You just look at the crowds that come to his rallies. We just have to make sure they vote,” said Leslie Sexton, a 70-year-old retired union representative, who drove 4½ hours from her home in Dayton, Nev., to help out at the event.

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Mr. Sanders’s campaign has used a horizontal organizing structure to co-ordinate volunteers taking “Bernie Journeys.” A portal on Mr. Sanders’s website directs people to priority canvassing locations in key states. There are also online spreadsheets to connect travelling volunteers with locals willing to put them up and with carpools between cities. A Slack channel allows people to team up to share housing and transportation. Organizers use nightly webinars to brief volunteers and answer questions.

Angie Rhoten, a stay-at-home mother from Albuquerque, N.M., travelled first to Iowa to serve as a precinct captain for Mr. Sanders at a caucus. Then, she went to South Carolina to canvass. Next, she’s headed to Louisiana, which votes on April 4.

The 49-year-old rhymed off several personal reasons she was backing the Senator. Ms. Rhoten’s husband is a veteran of the Iraq and Afghanistan wars with post-traumatic stress disorder, her daughter is a single parent with US$26,000 in university debt and her daughter’s boyfriend is an immigrant from Mexico.

“I’ve never seen a movement like this. Other campaigns don’t have this sort of energy,” she said.

Dan Escola, a 41-year-old airline pilot from New York who was canvassing the same suburb as Mr. Masson, said Mr. Sanders’s commitment to essentially the same agenda since the 1960s was a powerful motivator.

“I really appreciate how consistent Bernie has been for so long,” he said. “It’s sad that we’re such a powerful, rich country and we don’t provide for everyone.”

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Mr. Escola has been able to fly at no cost between campaign stops, thanks to a perk of his job. A more common trajectory is Mr. Masson’s.

A Regina native who graduated from the University of Ottawa in December, Mr. Masson decided to join Mr. Sanders’s campaign after seeing an Instagram post from him calling for volunteers. Mr. Masson took a bus to New Hampshire and split a motel with another volunteer he met on Slack. After that, he got a ride to New York and bused down to South Carolina. Next, he was catching a lift to Florida with another supporter who was also putting him up in Orlando.

The United States isn’t his country, but he feels a stake in the result.

“If they make college free in the U.S., like Bernie is proposing, that would put pressure on Canada to do it as well. The current President doesn’t believe in climate change; that matters for all of us,” he said. “U.S. politics affect the whole world.”

Editor’s note: In a previous version, Dan Escola's name was spelled incorrectly.

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