A giant banner of Brazil’s incarcerated former president Jair Bolsonaro fluttered in the morning breeze as his eldest son, Flávio, touched down at an airfield on the fringe of a city that will soon help decide the future of one of the biggest democracies on earth.

“Brazil is rudderless. Brazil has no president and Brazil needs a president – and that president is Flávio Bolsonaro,” the far-right senator declared as he waded into the flock of supporters who had gathered to welcome him to Juiz de Fora, one of the largest cities in the battleground state of Minas Gerais.

With less than a month before nearly 159 million Brazilians choose their next leader on 4 October, the election appears on a knife-edge, with the incumbent leftwing president, Luiz Inácio Lula da Silva, and his challenger, Flávio Bolsonaro, neck-and-neck in the polls.

Bolsonaro’s campaign appears to have seized the momentum in recent weeks amid a slew of corruption scandals involving Lula’s son and the supreme court. That has prompted despair among progressives who fear their country could fall back into the hands of a radical rightwing movement that tried to grab power after the then-president, Jair Bolsonaro, lost the 2022 election to Lula.

Last September, Jair Bolsonaro received a 27-year jail sentence for spearheading that botched coup – a verdict supporters insist was unjust. But the ex-president and his accomplices are likely to be freed if his son wins power – a prospect that delights the hardcore Bolsonaristas who turned out to greet Flávio Bolsonaro wearing yellow football shirts and headbands reading: “Lula out!”

“Today is a moment of joy,” said Ulisses Lima, 50, a cybersecurity specialist with a Jesus Christ pendant around his neck. “Flávio represents change. He represents Brazil’s rescue from this socialist abyss we’ve spent so long warning about,” Lima added as supporters waited for the former president’s heir to arrive.

Nearby, another devotee, José Caldeira, fell to his knees and begged for divine intervention to get Bolsonaro out of house arrest. “God, free this nation! Amnesty and freedom for Bolsonaro!” Caldeira bellowed, raising his hands towards the sky.

A third man, Davi Frederico, held a banner celebrating Donald Trump, who has been accused of trying to swing the election in Bolsonaro’s favour through economic and diplomatic pressure. “Make Liberals Cry Again,” it said.

Juiz de Fora, an industrial and university city traditionally associated with the left, is also a key location for Brazil’s hard right. The city’s army headquarters was the launchpad for the 1964 coup that plunged Brazil into two decades of military rule. And it was in Juiz de Fora, on the eve of the 2018 election, that Jair Bolsonaro was stabbed in the gut while campaigning – an attack widely believed to have helped the former paratrooper seal his victory.

Bolsonaro’s shock win ushered in what, from a progressive perspective, were four abysmal years. Destruction of the Amazon rainforest and gun ownership skyrocketed, hundreds of thousands died during a Covid outbreak Bolsonaro was accused of mishandling, and the president’s authoritarian rhetoric and attacks on Brazil’s electronic voting system culminated in the 8 January 2023 riots in Brasília. The supreme court later called those disturbances part of a plot to “annihilate” the country’s democracy.

But the Bolsonaros still enjoy abundant support, and that devotion was visible as Flávio Bolsonaro’s motorcade crept towards the high street where his father was ambushed eight years ago.

“Let’s get the left out! Let’s get these motherfuckers out!” one elderly woman shrieked as the senator passed by on top of a sound truck stamped with the word: “Jesus”. Other fans, many senior citizens, waved Brazil flags from windows or stood on the sidewalk flashing victory signs with their hands.

“Barring some kind of leftwing trickery, Flávio Bolsonaro can already be considered president. All you have to do is take a look at the streets and social media,” claimed Nikolas Ferreira, an influential far-right congressman from Minas Gerais who has more than 9 million TikTok followers.

Alongside the enthusiasm, there were glimpses of the revulsion many Brazilians feel for the former president. One leftwinger took to his balcony with a loudhailer to taunt the Bolsonaristas as they paraded through town. “Trump! Trump! Get my daddy out of jail!” the dissenter jeered in reference to the US president’s attempts to help Bolsonaro escape punishment.

Minas Gerais, a mountainous mining and agricultural region that is larger than France and has 21 million inhabitants, is Brazil’s bellwether state. Since democracy returned in the 1980s, no candidate has won the presidency without triumphing here. In 2018, Jair Bolsonaro beat Lula’s candidate in Minas by more than 1.7m votes. Four years later, Lula reclaimed the state by fewer than 50,000. After landing in Minas last week, Flávio Bolsonaro said he was confident of clawing back the swing state, with one recent poll putting him ahead there.

“[Lula] is a president who you look at and see the past,” the 45-year-old senator said of his 80-year-old adversary. “With Flávio you can be sure that when people look at him, they see a modern government and a government of the future.”

Thomas Traumann, a political analyst who has written a book about his polarised country, said the election was too close to call. “It’s a coin flip,” said Traumann, who believed an unexpected scandal or last-minute “black swan” event could swing the election either way. On Friday, it emerged that Flávio Bolsonaro had been placed under police investigation over suspicions of corruption involving the funding of a big-budget biopic telling the story of the assassination attempt against his father in Juiz de Fora.

For progressive voters, the vision for a Flávio Bolsonaro administration laid out during his visit to Minas is the stuff of nightmares. “I think Flávio Bolsonaro’s presidency is going to be Jair Bolsonaro 2.0,” said Bruno Engler, a Bolsonarista lawmaker from Minas’ capital, Belo Horizonte.

Engler believed a top priority would be zero-tolerance policing, with the younger Bolsonaro pledging an iron-fisted crackdown on criminals his father has compared to cockroaches. “Thugs who don’t surrender will be arrested or neutralised,” Engler vowed, predicting gun laws would be loosened.

Speaking on the street corner where his father was knifed, Flávio Bolsonaro vowed to pack Brazil’s 11-member supreme court with five conservative judges “who are against abortion [and] against drugs”. “We’re going to give the streets back to the Brazilian people … We’re going to lower the age of criminal responsibility. We are going to introduce chemical castration for rapists,” shouted the candidate, who wore a bullet-proof vest.

Those pledges prompted whoops of excitement from the crush of supporters below Bolsonaro’s truck. Dozens ofmobile phones captured the candidate’s every word. But amid the rightwing rejoicing there was fear and trepidation, too.

Lennon César, a law student and leftwing activist who had come to confront Bolsonaro’s fans, voiced incredulity that less than four years after Jair Bolsonaro’s failed power grab, tens of millions of Brazilians seemed poised to vote for his son.

“We were the victims of an attempted coup – and his father was the perpetrator,” recalled César, 28. “It’s terrifying. And the thing that worries me most is that the general public doesn’t really seem to get what’s happening. Brazilians have short memories when it comes to the past.”

As a black, gay man, César felt particular dread at the prospect of a second Bolsonaro presidency, given the patriarch’s hostility to minorities.

César vowed to vote for Lula, Brazil’s first working-class president, calling him the only leader who paid attention to the poor. “If today I’m studying for a law degree it’s because one of Lula’s government programmes allowed me to achieve that,” he said, warning: “These people … might destroy it all.”

A few blocks away, a graffiti artist had spray painted their own message of disapproval on to the facade of Bolsonaro’s Juiz de Fora HQ. “Facists [sic],” it read.