In the 1980s, a French punk rock band coined a rallying cry against the country’s far right that retained its punch over decades. The chant, still shouted at protests by the left, is “La jeunesse emmerde le Front National,” which cannot be translated well without curse words, but essentially tells the far right to get lost.

That crude battle cry is emblematic of what had been conventional wisdom not only in France, but also elsewhere — that young people often tilt left in their politics. Now, that notion has been challenged as increasing numbers of young people have joined swaths of the French electorate to support the National Rally, a party once deemed too extreme to govern.

The results from Sunday’s parliamentary vote, the first of a two-part election, showed young people across the political spectrum coming out to cast ballots in much greater numbers than in previous years. A majority of them voted for the left. But one of the biggest jumps was in the estimated numbers of 18-to-24-year-olds who cast ballots for the National Rally, in an election that many say could reshape France.

A quarter of the age group voted for the party, according to a recent poll by the Ifop polling institute, up from 12 percent just two years ago.

There is no one reason for such a significant shift. The National Rally has tried to sanitize its image, kicking out overtly antisemitic people, for instance, who shared the deep-seated prejudice of the movement’s founder, Jean-Marie Le Pen. And the party’s anti-immigrant platform resonates for some who see what they consider uncontrolled migration as a problem.

The party also benefits from the passage of time; many of the young people backing the National Rally were toddlers, or not even born, when Mr. Le Pen shocked France by reaching the 2002 presidential runoff.

And the National Rally was savvy in its choice of a new face: Jordan Bardella, a charismatic 28-year-old with an impressive TikTok following who took over as its president from Mr. Le Pen’s daughter Marine in 2022. He has helped clean up the party’s racist image while also pushing for preferential treatment for French citizens over even legal migrants.

“We are from a generation that never knew Jean-Marie Le Pen,” said Enzo Marano, 23, the head of a local National Rally youth chapter who was recently handing out the party’s fliers in a Paris suburb. “We are the Bardella generation.”

Mr. Bardella, analysts say, embodies the final stages of the National Rally’s decades-long efforts to rebrand itself — harnessing social media to reach young voters and repackaging its message into a slick social media campaign centered on him.

Focusing on Mr. Bardella is a crucial tactic for the party, whose founders included former Nazi collaborators and some of whose members still come under fire for racist or antisemitic comments.

“When you talk more about the party itself, you have to talk about that party’s history and its ideology,” said Laurent Lardeux, a sociologist at the National Institute of Youth and Popular Education. But when the campaign centered on a person, he added, “You can set ideology aside and talk much more about character, posture — it’s branding and communication.”

That strategy, combined with growing anger against President Emmanuel Macron, appears to have worked so far. The National Rally trounced Mr. Macron’s party in recent European parliamentary elections, a poor showing that led him to call snap elections for France’s Parliament.

But his gamble that the nation would shift back to the center appeared to fail when the National Rally dominated that election, too, which heads to a runoff for most seats this weekend.

The far right’s growing popularity has alarmed the left, which is still the choice of most young voters. The New Popular Front, an alliance of left-wing parties, got 42 percent of the votes of people age 18 to 24 on Sunday, more than any other group, according to Ifop.

Left-wing activists are now working hard to get out the vote for this Sunday’s runoff.

“We don’t have a choice,” Amadou Ka, a candidate for the New Popular Front, said recently while campaigning in Creil, a town about 30 miles north of Paris.

The participation rate for people age 18 to 24 surged to 56 percent during the first round of voting, up from 25 percent in 2022, according to Ifop.

Analysts say young people are more likely to vote when a lot is at stake, as is the case in this election, which could bring the National Rally to power for the first time. If the party were to win an absolute majority, Mr. Macron would be forced to appoint Mr. Bardella as prime minister, giving him control over domestic policy.

For those who support the right, this is the National Rally’s big chance.

“We are at power’s doorstep,” Mr. Marano said as he passed out campaign material.

Some people were openly hostile, crumpling the leaflets and angrily referring to the party’s antisemitic and racist past. “This, to me, is fascism,” one older man said in broken French, pointing to a leaflet featuring a beaming Mr. Bardella.

Olivier Galland, a sociologist at the National Center for Scientific Research, said Mr. Bardella appealed to young working-class voters, many in rural areas, who often struggled to secure stable jobs.

“Bardella embodies that part of France’s youth that feels forgotten by traditional politicians,” he said.

Noah Ludon, 19, a history student who joined the National Rally this month, said he identified with Mr. Bardella because they both grew up in middle-class families in Parisian suburbs with large immigrant populations.

“I don’t feel at home anymore,” Mr. Ludon said, referring to an influx of migrants. “Finding a French butcher has become hard.” Asked to elaborate, he said he meant a butcher that was not halal.

Mr. Ludon, who said his mother had been assaulted in a supermarket parking lot, said crime was also a big concern.

Such statements echo Mr. Bardella’s talking points, shared with his more than 1.8 million followers on TikTok. Although other French politicians are also on TikTok, Mr. Bardella is known for being particularly adept and gets more likes and comments than other politicians — even those like Mr. Macron who have far more followers.

“He is good at balancing serious and lighter content, surfing on trends, showing a personal side,” said Marie Guyomarc’h, a spokeswoman for Visibrain, a company that analyzes social media. “He’s not the only one,” she added, “but he’s the only one for whom it has worked so well.”

Many of Mr. Bardella’s videos address classic far-right talking points like crime and immigration. But other clips have little to do with policy.

In some of Mr. Bardella’s most popular videos, he alludes to spoof video montages that toy with the notion that he and Gabriel Attal, Mr. Macron’s prime minister, are secretly in love — a winking rejoinder to his followers that he knows what they are posting, and has a sense of humor about it. On social media he has also referenced the video game Call of Duty, which, according to a profile in Le Monde, he used to play as a teenager.

In other words, he is one of them.

It is just that chumminess, and the far-right agenda he is working to humanize, that frightens many young people from immigrant backgrounds or who belong to ethnic minorities.

Rania Daki, 21, a student and activist who grew up in Aubervilliers, a Paris suburb, said that talk of Ms. Le Pen scared her as a child — back then, she recalled, those who supported the far right did so in hushed tones.

“Now, it has become completely normal,” Ms. Daki said.

She and two friends have written an open letter in the newspaper Libération urging working-class neighborhoods to vote and have been knocking on doors to get out the message.

But she said the outreach has been hard. Many young people said they were disillusioned by politics. Others said they didn’t follow the news.

Worries over discrimination and police violence are particularly strong in the places she canvassed. The National Rally wants to create a legally mandated “presumption of self-defense” for law enforcement, which activists worry will make it even harder to hold officers accountable in police violence often directed against people of color.

So when the far right’s percentage of the vote appeared on a television screen on Sunday in the offices of Ghett’up, a community organizing association in the multicultural Paris suburb of Saint-Denis, there was a gasp.

“Even before these results, people were attacked, insulted and spit on,” said Mariam Touré, 22, a law student and community activist who was at the event. Her family fled civil war in Ivory Coast in 2009.

“They will never erase us from the political landscape,” Ms. Touré defiantly told the attendees. “At the same time,” she added, her voice cracking, “I am very scared.”