Hundreds of demonstrators had swarmed around Buenos Aires’s iconic Obelisk to champion the man they call “El Peluca” – the Wig. “You can feel it! You can feel it! Peluca presidente!” the marchers chanted of their wild-thatched leader, the far-right populist Javier Milei. Among the crowd was Esteban Elías Lozupone, a 48-year-old taxi driver who had brought his daughter to witness the pro-Milei rally on the eve of one of Argentina’s most crucial presidential elections in decades. “We’re trying to change things. Otherwise this country won’t progress,” said Lozupone whose 11-year-old wore a rattlesnake Gadsden flag – a symbol of Milei’s movement and the US far right – around her neck. Like millions of Argentinians, Lozupone is electrified by the prospect of Milei winning Sunday’s election – believing the anti-establishment economist can haul the South American country out of years of financial misery with radical measures including abolishing the central bank and dollarising the economy. Polls suggest Milei enjoys a slender advantage over his opponent, the centrist finance minister, Sergio Massa, whose Peronist administration is widely blamed for plunging Argentina into its worst economic crisis in two decades. But as election day nears, Lozupone is also worried, having embraced conspiracy theories, being fanned by Milei’s campaign, that October’s first round was rigged – and Sunday’s election may be too. “I think there was a lot of fraud,” the taxi driver claimed, without proof, of last month’s contest, which Milei unexpectedly lost to Massa by nearly 2 million votes. Darío Rodríguez, a 26-year-old food service worker who was also at the pro-Milei “anti-fraud” march, parroted a piece of fake news that has circulated on social media accounts linked to the rightwing libertarian. According to it, Massa won every single vote in the northern province of Santiago del Estero in the first round. “Isn’t that odd?” Rodríguez asked. In reality, Milei won nearly 23% of votes there. The proliferation of conspiracies and fabrications about electoral fraud is eerily reminiscent of what happened in the US and Brazil under Donald Trump and Jair Bolsonaro, rightwing populists to whom Milei is often compared. In the lead-up to the 2020 US election, Trump made hundreds of false or misleading claims about the vote and, after losing to Joe Biden, refused to concede, falsely alleging the election had been stolen. Before Brazil’s 2022 election, Bolsonaro repeatedly undermined the reliability of his country’s electronic voting system and, after losing to Luiz Inácio Lula da Silva, also refused to accept the result. Both countries subsequently suffered severe outbreaks of violence after Trump and Bolsonaro supporters – infuriated by bogus claims of fraud – ran riot in their respective capitals, seeking to overturn the results. Milei, who has promoted conspiracy theories blaming leftists for the violence in Brasília, seems to be following a similar script in Argentina. On Tuesday, senior representatives of Milei’s party, Libertad Avanza (Freedom Advances), filed a petition to an electoral judge demanding “legality and transparency” in the election and accusing members of Argentina’s military police, the gendarmerie, of “colossal fraud” during the first round. According to the petition, the agents, who provide security during the electoral process, “changed the contents of the ballot boxes” in the hours after the vote to boost support for Massa. The petitioners – Libertad Avanza’s lawyer, Santiago Viola, and Milei’s sister and campaign manager, Karina Milei – offered no proof. “We don’t have any videos or photos,” Viola admitted in an interview. “But the testimonies are credible – we have an inside source from the gendarmerie,” he claimed. Viola and Milei called for the navy and air force to be tasked with ensuring Sunday’s vote was not affected by “unscrupulous people” committing “illegal acts”. Argentina’s security minister, Aníbal Fernández, said he would seek to bring criminal charges against Milei’s party over its “foolish” accusations. Earlier this month Milei claimed, also without evidence, that the first round was “not clean” and had suffered “irregularities of such a size that put the result in doubt”. After winning August’s primary – which serves as a dress rehearsal for the election, Milei alleged – again without evidence – that ballots had been stolen from polling stations, depriving him of votes. “There are places where we had zero votes,” Milei said. “That’s weird.” Such interventions have convinced many that the Argentinian populist could refuse to accept a narrow election defeat, as Trump and Bolsonaro did in the US and Brazil. “It’s very difficult to say what Milei will do [if he loses] but it’s highly probably that he will follow this … wannabe fascist playbook,” said Federico Finchelstein, an Argentinian historian who has written extensively about far-right populists including Bolsonaro and Trump. Ariel Goldstein, the author of a recent book about the revival of Latin America’s authoritarian right, said peddling conspiracies about election fraud was an effective way of mobilising far-right supporters and meshed with Milei’s claim to be an honorable corruption-busting outsider battling an evil-intentioned political “caste”. “This ‘caste’ idea that Milei has spread – that politicians are corrupt enemies we must destroy – connects very well with the fraud theory. [It’s:] ‘The caste commits fraud.’ They are two conspiracy theories that fit with the idea that there is an enemy which operates in the shadows,” Goldstein said. Neither academic thought Milei – who unlike Trump and Bolsonaro, has not previously served as president – was strong enough to try to forcefully overturn an election result by encouraging a Brasília or Washington-style revolt. “I don’t see Milei being able to have the support that Bolsonaro and Trump had … for this kind of adventure,” said Finchelstein. “[Trump and Bolsonaro] had years in power to cement their power and their legitimacy with state actors. At this point, I don’t see that in Javier Milei, especially regarding the security apparatus.” Even if Milei did attempt some kind of anti-democratic rupture, Goldstein believed he would lack the “surprise element” supporters of Trump and Bolsonaro enjoyed when they launched their failed insurrections. He believed Massa’s campaign would be alert to any such plot given last January’s attempt to topple Lula’s government in neighbouring Brazil. “Some of Massa’s advisers are Brazilian and worked on Lula’s campaign last year,” Goldstein said. “So everything seems to indicate that they are more aware of how the far right operates in other countries and how it could operate in Argentina.” Still, experts fear any attempt to challenge the election would accelerate a worrying erosion of democratic norms, which has also seen Milei and his ultra-conservative running mate, the congresswoman Victoria Villarruel, question the four-decade consensus over the crimes of Argentina’s 1976-83 dictatorship, which is estimated to have killed about 30,000 people. Milei and Villarruel, who he has said will serve as his government’s security and defence chief, have both downplayed the number of victims and characterised the bloodshed as part of a justifiable war against regime opponents. This week Villarruel caused outrage after declaring that the solution to Argentina’s crisis was “tyranny”. “It’s extremely worrisome that this kind of extreme, radical individual would be in charge of security and the state monopoly of violence,” Finchelstein said of Villarruel, whose uncle was an intelligence officer who worked at a secret jail during the dictatorship. In an election-eve editorial, the Buenos Aires Herald wrote: “Even if [Milei] loses, the cost of his political rise has already been immense. “He has emboldened the most dangerous elements of the far right, resulting in attacks on minorities, demonization of the poor, and an institutionalization of hate speech. This is one of the greatest challenges for Argentine democracy,” the newspaper added. Were Milei to win Sunday’s election, Finchelstein believed Bolsonaro’s Brazil provided a useful roadmap for what Argentina might look like. He feared there would be attacks on democratic institutions, that minorities and political opponents would be demonised and gun laws loosened as happened over the border. Radical austerity measures would probably fuel inequality and poverty and spark unrest on the streets of Buenos Aires. “The Brazilian past with Bolsonaro resembles the possibility of an Argentinian future,” Finchelstein warned, predicting: “If Milei wins, democracy will suffer.”