Javier Milei wants to be Argentina’s next president. But first he must get around legions of angry Taylor Swift and BTS fans.Javier Milei, a far-right libertarian economist, has stayed aloft in Argentina’s presidential campaign on the wings of the youth vote.To win the runoff election this month, he will need to hold on to that key demographic, pollsters say. But now, a major hurdle stands in his way: Swifties.Squadrons of Argentine fans of the pop star Taylor Swift have gotten political. They have trained their online sights on Mr. Milei and his rising libertarian party, framing them as a danger to Argentina, while Ms. Swift herself is preparing to arrive in Argentina next week for the launch of her Eras Tour outside North America.“Milei=Trump,” said one post from a group called Swifties Against Freedom Advances, which is the name of Mr. Milei’s party.After Mr. Milei placed second in Argentina’s election last month, sending him to a runoff on Nov. 19, a group of 10 Argentine fans of Ms. Swift created the group and issued a news release calling on fellow fans to vote against Mr. Milei. They said they were inspired by Ms. Swift’s past efforts to confront right-wing politicians in the United States.Mr. Milei placed second in Argentina’s election last month, sending him to a runoff on Nov. 19. Polls have indicated that Mr. Milei is especially popular with young voters.Sarah Pabst for The New York Times“We cannot not fight after having heard and seen Taylor give everything so that the right doesn’t win in her country,” the group said in the statement. “As Taylor says, we have to be on the right side of history.”The two-page missive was viewed 1.5 million times on X, the site formerly known as Twitter, before it suspended the group’s account without explanation, the group said.In the statement, it called Mr. Milei’s positions against legal abortion, his support for the loosening of gun laws and his proposals to overhaul public education and public health care as “a danger to democracy.”The statement also took aim at Mr. Milei’s comments that criticized feminism, claimed a pay gap between men and women does not exist and referred to the atrocities committed by Argentina’s military dictatorship from 1976 to 1983 as simply “excesses.”Mr. Milei, in response, has shrugged off the Swifties. “I’m not the far right,” he told a radio station. “They can express what they want.” His campaign declined to comment.Ms. Swift, who will perform the first of a series of three sold-out shows in Buenos Aires on Thursday, has not commented publicly on the Argentine election.The Swifties’ criticism of Mr. Milei has shifted the conversation to his conservative social views and away from his drastic proposals to reverse Argentina’s economic crisis, which include ditching the Argentine peso for the U.S. dollar and closing the country’s central bank.A fan of Ms. Swift wearing a bracelet bearing the name of Mr. Milei’s opponent, Sergio Massa. Ms. Swift will perform the first of a series of three sold-out shows in Buenos Aires on Thursday.Anita Pouchard Serra for The New York TimesBut it isn’t just Swifties who are organizing against Mr. Milei. He and his running mate, Victoria Villarruel, are also contending with criticism from legions of loyal fans of another musical juggernaut, the K-pop band BTS. They are so active and organized on the internet that they have become known as the BTS Army.Last week, the fury of that army was unleashed upon Ms. Villarruel after a series of her tweets denigrating the K-pop group resurfaced. In 2020, she likened the name BTS to a sexually transmitted disease. She also mocked the dyed pink and green hair of some members.Those tweets prompted such a fierce response from BTS fans, accusing her of xenophobia, that a large BTS fan club in Argentina felt compelled to try to calm their fellow fans down. “The message that BTS always transmits is one of respect to oneself and everyone else,” said a statement from the club, which has been viewed 1.9 million times, according to X.Ms. Villarruel’s only reaction online to the BTS blowback has been a post in which she called her S.T.D. post part of “funny chats” from “a thousand years ago.”Mr. Milei’s political base is particularly reliant on young voters. One survey of 2,400 people in October showed that nearly 27 percent of his support came from people ages 17 to 25, versus less than 9 percent for Sergio Massa, the center-left economy minister who opposes Mr. Milei in the runoff. People under 29 account for 27 percent of all eligible voters in Argentina.Many young voters said they see Mr. Milei, who has taken to wearing leather jackets and wielding a chain saw at his campaign events, as the “cool” outsider candidate who has also become a sort of online meme.“The majority of people our age, from about 16 to 25, are voting for him,” said Mateo Guevara, 21, a student who attended a Milei rally last month in Salta, a northern city. “He is a guy that came out of nowhere.”Mr. Milei and Mr. Massa appear to be headed toward a close contest. A poll published Friday by Atlas Intel showed that Mr. Milei had a lead of four percentage points, with a margin of error of two points.Mr. Massa holds a slight lead over Mr. Milei, according to a recent poll.Marcos Brindicci/Getty ImagesMs. Swift shunned politics for most of her career. But in 2018 she broke her silence to oppose the Republican Senate candidate Marsha Blackburn in Ms. Swift’s home state, Tennessee, helping to trigger a spike in young-voter registrations in the U.S. midterms that year.Ms. Swift said she felt compelled to speak out against Ms. Blackburn, who was endorsed by former President Donald J. Trump, because the politician’s record “appalls and terrifies me,” including positions on equal pay for women, violence against women and gay rights. Ms. Blackburn wound up winning.Ms. Swift’s song “Only the Young,” a rallying cry that describes young people as agents of change, was featured in an ad from Representative Eric Swalwell, a California Democrat, in a push to get out the vote in 2020.And Ms. Swift’s comments in a 2020 documentary, in which she said she had decided to publicly oppose Mr. Trump despite the risk to her career, have been circulating widely in Argentina in recent weeks.BTS fans are their own political force, having most likely helped suppress turnout at a Trump rally in Tulsa, Okla., in 2020 by reserving seats and not showing up.Outside the River Plate soccer stadium in Buenos Aires, where Ms. Swift will perform next week, a contingent of Swifties has been camping out to see the show. Many said they were not eager to mix politics with music.“The reality of the United States is a very different reality than the one that we are living here,” said Barbara Alcibiade, 22, a pastry chef. “It’s true that a large percentage of fans may or may not follow certain ideals or the values that she represents, but that doesn’t mean that represents everyone.”Barbara Alcibiade, 22, who has been camping out near the stadium where Ms. Swift will perform, said that the political actions of some Swifties didn’t represent all of her fans. Anita Pouchard Serra for The New York TimesThe Swifties behind the anti-Milei news release said they never claimed to speak for Ms. Swift or all her fans. “That’s why we were very careful not to say that Taylor wouldn’t vote for Javier Milei,” said one member, Macarena, 29, who declined to give her last name because she said the group had received threats online.But for Macarena and her friends, the parallels between Mr. Milei and Mr. Trump are clear.“There isn’t any Taylor statement that you can use to say that I’m going to vote for a candidate from the far right,” she said.At a K-pop dance school in Buenos Aires, BTS fans said the 2020 comments by Mr. Milei’s running mate disparaging the group served only to reinforce their aversion to Mr. Milei.“It was really upsetting because it’s always the same thing, xenophobic attacks, treating them as if they’re different,” said Marcela Toyos, 36, a teacher, after dancing to the BTS hit “Mic Drop.”Macarena said she and her friends now have a WhatsApp group of 140 Swifties in Buenos Aires that is planning to put up posters opposing Mr. Milei outside Ms. Swift’s concerts next week. The Swifties are also coordinating with smaller groups in other provinces, she said.Ahead of Ms. Swift’s arrival, the Buenos Aires Legislature voted Thursday to name Ms. Swift a guest of honor. The only officials to vote against the proposal were members of Mr. Milei’s party.Jack Nicas More