Corruption is a major concern for many Brazilian voters ahead of the October 25 presidential runoff between far-right candidate Flávio Bolsonaro and left-leaning Luiz Inácio Lula da Silva. However, experts say its biggest impact may be on voter turnout rather than on the choice between the two candidates.

Both candidates are associated with corruption allegations in the minds of many Brazilians. Bolsonaro is under investigation for corruption, money laundering and tax evasion, while Lula spent 19 months in prison on corruption and money laundering charges that were later annulled.

For committed supporters of either candidate, such allegations are unlikely to weaken their loyalty. But experts warn that widespread perceptions of corruption could increase voter abstention and anti-incumbency sentiment, potentially benefiting Bolsonaro, who received 2.2 million more votes than Lula in the first round.

Brazil is deeply polarised, with supporters of the two candidates viewing the opposing camp with considerable distrust. During the first round, many voters wore red clothing to signal support for Lula’s party, while others donned the green and yellow of the Brazilian flag, adopted by Bolsonaro’s movement.

Such political divisions make voters less likely to give weight to corruption allegations against their preferred candidates, experts say.

“We have a great ability to filter information that goes against our beliefs,” said Nara Pavão, a political science professor at the Federal University of Pernambuco. “People don’t want to discover the truth about their candidates, they want to beat the opponent.”

Camila Tobji de Aquino, a 19-year-old student of pedagogy and psychology, considers corruption a problem across political parties. However, she sees Bolsonaro as a threat to democracy.

“If I were to vote only for a candidate not tied to any corruption, I would vote blank,” she said. “But that’s not the choice Brazil is facing. For me it’s a question of being able to vote in the next election.”

Corruption has dominated public debate in the run-up to the election, with a major scandal involving politicians and judges at Brazil’s Supreme Court drawing particular attention.

Justice Alexandre de Moraes, who presided over the legal case that led to former president Jair Bolsonaro’s imprisonment for attempting a coup, is suspected of having links to the former head of the failed Banco Master bank. Flávio Bolsonaro has also been linked to the scandal. Both have denied wrongdoing.

The Banco Master affair has revived memories of Operation Car Wash, Brazil’s largest corruption and money-laundering investigation, launched in 2014, which implicated dozens of politicians.

Repeated scandals could discourage undecided voters and increase abstention, said Laura Chelidonopoulos, a political science PhD candidate at the University of Pittsburgh who has studied corruption.

“People become disenchanted with politics,” she said. “They have less motivation to actually choose between one of these two sides.”

More than 33 million people, or 21% of Brazil’s electorate, did not vote on October 4, marking the highest first-round abstention rate since 1998. First-round abstention has gradually increased since 2006, according to data from Brazil’s electoral court.

For some voters, disillusionment with politics has already led them to stay away from the polls.

José Tainan, a 36-year-old kitchen assistant from Rio de Janeiro’s Penha favela complex, said he struggled to remember the last time he voted, although he believed it was for Lula in the 2000s. He cited corruption as the main reason he stopped voting.

“There are no good options. Neither one of them suits me. I would rather justify why I didn’t vote,” he said.

Voting is compulsory in Brazil for citizens aged 18 to 70, with those who fail to vote without a valid reason facing a small fine.

Matusalem Aguiar, a 54-year-old taxi driver from the impoverished municipality of Belford Roxo near Rio de Janeiro, said he would prefer political candidates to have clean records. Nevertheless, he plans to vote for Bolsonaro despite the investigations against him, saying the country needs change.

“There needs to be a change,” Aguiar said. “Some people have a lot of power and they’re not managing the country in the right way.”