When Steve Bannon described Brazil’s 2022 presidential election as the “most important of all time in South America”, the former Trump adviser had at his side a man as close as anyone to Brazil’s president Jair Bolsonaro — his son Eduardo.

Introduced by Bannon at an event in South Dakota last year as the “third son of Trump from the tropics”, Eduardo has become his father’s trusted international envoy and ideologue, forging close ties to overseas conservative allies such as the Trump family.

With Jair Bolsonaro facing an uphill battle to win a second term in October, in an election considered a critical test for democracy in Latin America’s biggest nation, Eduardo has joined his father in questioning Brazil’s electronic voting system and casting doubt on the supreme court.

A former two-term president, leftwinger Luiz Inácio Lula da Silva, is leading almost all polls by a wide margin but Eduardo believes the race is “tied”.

“I do not trust the polls,” he says in his cramped lawmaker’s office in Brasília.

Nicknamed “03” by his father in reference to his older brothers, senator Flávio and Rio councillor Carlos, Eduardo initially shunned politics. He served in Brazil’s federal police before winning a São Paulo congressional seat in 2014 at the age of 30.

“We spent about $10,000 and I got elected,” he says in a rare interview. “It was really lucky.” Four years later he set an election record, winning the highest number of votes of any lower house deputy, 1.84mn.

Eduardo comes across as friendly and courteous, but his remarks are not always charitable. He spends at least as much time attacking the supreme court as he does lambasting his father’s main rival for the presidency.

The justices are “fighting against” his father by intervening “all the time” in favour of Lula, he says.

With a broader mandate than many global peers, Brazil’s top legal body can open its own investigations as well as judge appeals. Many Brazilians see the court as a bulwark of democracy. But for Bolsonaro, his sons and the country’s right wing, it represents a leftist establishment resisting the president’s conservatism.

“In dictatorships they close press, they put journalists in jail, they exile people, they arrest presidents of parties, they arrest politicians,” Eduardo said. “Everything that I said is happening in Brazil but not [at] the hands of President Bolsonaro, [at] the hands of the supreme court.”

He cited Daniel Silveira, a former military policeman turned Bolsonarista congressman, who became a hard-right cause célèbre. The supreme court sentenced Silveira to nearly nine years in prison in April after the politician threatened justices including Alexandre de Moraes in online posts. One said: “The people need to go to the Supreme Court, grab de Moraes by the neck and throw his little egg head in the garbage.”

Eduardo did not condemn Silveira and described the supreme court’s behaviour as “disgusting”. De Moraes “says he’s the victim, he [makes] the accusations and he judges the case . . . so it’s a unique system we have here in Brazil”. His father ordered a presidential pardon for Silveira.

Eduardo’s command of English, acquired during a work exchange programme in the US, and his ideological convictions helped make him the bridge between Bolsonaro and his allies abroad. The president tried in 2019 to name his son as Brazil’s ambassador in Washington but backed down after congressional opposition.

Eduardo says he admires Trump “a lot” and the sentiment seems mutual. On his office wall is a framed copy of Eduardo’s Wikipedia entry with a handwritten endorsement from the former US president: “Eduardo, you are great. Big statement on your wonderful father will be coming soon — best wishes, Donald.”

“He has a unique gift for channelling America’s conservative movement, with a Brazilian twist,” said Gerald Brant, a US-based financier close to the Bolsonaro family. “He will carry his father’s mantle far.”

Eduardo was in Washington during the January 6 attack on the Capitol by Trump supporters but declines to comment on the insurrection, saying it is “an internal issue” for Americans. He has since held further meetings with Trump family members and allies, including last August’s South Dakota conference attended by Bannon.

Tom Shannon, a former senior state department official who specialises in Latin America, said he understood that Eduardo “looked very closely at January 6 to understand what went wrong and why Trump was unsuccessful”.

“The real takeaway for them was that Trump depended on the mob to be successful,” Shannon said. “They believe . . . they need institutional support, they need the armed forces.”

President Bolsonaro’s attacks on the electronic ballot, repeated to a meeting of ambassadors in July, have prompted the Biden administration to express support for Brazil’s election system.

“We are completely confident that Brazil’s next election result will reflect the will of the voters,” said a senior state department official.

The president has claimed the computerised ballot machines are vulnerable to fraud and has called for the military to oversee a parallel vote count.

Eduardo ducks questions about what he and his father might do if the voting system is not changed and Jair loses the election. “I think they will improve [the voting system],” he says. “Everything else is futurologist thinking . . . I don’t know if [our supporters will] go to the streets.”

The prospect of violent protests concerns authorities. But Eduardo — whose office is adorned by toy firearm replicas and a sign saying “Gun safety rule #1: Carry one” — believes gun ownership, which has quadrupled under his father’s term, has made Brazil safer. He worries Lula would clamp down on firearms.

“Only dictators take people’s guns because they think the people are a threat,” he says. “We think the other way and would like to give to the people the possibility to defend themselves and their properties.”

For ‘03’, his father’s defence of such liberties defines his presidential term and builds the case for his re-election. “He was sacrificing his personal life to bring freedom to the Brazilians . . . he is a freedom fighter,” Eduardo says.