Brazilians will vote on Sunday in the most polarizing presidential election since the country’s democratization. In a contest that has seen fraud, aggression, misinformation, and violence, polls now predict a “tight” result between the right and the left. 

President Bolsonaro, a right winger, and President Lula da Silva, a leftist known as Lula who served two terms as president earlier this century, are more focused on sniping at each other than in promoting policies. Social media has amplified politically motivated violence that has spilled onto the streets.  

On Friday night, Messrs. Bolsonaro and da Silva participated in their final debate, during which the candidates bashed each other and launched accusations of lying to Brazilians. Mr. da Silva blamed the president for not increasing the minimum wage during his four years in office. Meanwhile, Mr. Bolsonaro brought up Mr. da Silva’s corruption history and alleged that the electoral system is against him. 

On Wednesday Mr. Bolsonaro’s Liberal party’s team took a page out of President Trump’s playbook by raising questions of election integrity even before the voting began. In court, Mr. Bolsonaro alleged that radio stations are boycotting him and declining to carry his campaign ads on the air. 

Rejecting the claim, the electoral court president, Alexandre de Moraes — who Mr. Bolsonaro earlier this year accused of being biased — said there was no sustainable evidence to the complaint. Mr. Bolsonaro’s intentions were to “provoke disturbances” less than a week before the elections, Mr. Moraes said.

On Wednesday night, Mr. Bolsonaro told journalists outside the Alvorada presidential palace that not having his campaign ads on air “unbalances” the democratic process. “The elections are close and my side suffers significant harm,” Mr. Bolsonaro said.

Election watchers now say that if Mr. Bolsonaro loses by a small margin and if he refuses to accept the result, violent street protests could result across the county. 

In the October 2 first round of elections, Mr. da Silva, who was in office as president between 2003 and 2010, was ahead with 48 percent of the vote to Mr. Bolsonaro 43.5 percent. The outcome was tighter than polls had predicted. About 46 million persons refrained from voting, the highest number since 1998. 

For the past month, both candidates have vied for support of the non-voters. They flooded Brazil’s southeast region with ads and conducted large campaign appearances. That part of the country boasts the three most populated states — Rio de Janeiro, São Paulo, and Minas Gerais. 

According to Brazil’s largest polling firm, Datafolha, Mr. Bolsonaro is leading in São Paulo and Rio de Janeiro with 49 percent and 51 percent of the votes, compared to Mr. da Silva’s 43 percent and 41 percent. However, the leftist candidate is leading in Minas Gerais with 48 percent of the votes, against Mr. Bolsonaro’s 43 percent. 

A political consultant, Leonardo Barreto, told the Argentinian paper La Nacion that the southeast states are the “swing states of Brazil” and that their support could turn an election. 

Each candidate has had his own goals during their campaign. Mr. Bolsonaro has been dodging controversies, including, most recently, when a former ally, Roberto Jefferson, shot at police officers. Mr. da Silva, meanwhile, has been trying to rekindle his supporters’ hope for a return to the “economic boom” of his days in office. He also tried to lure in evangelicals by flip-flopping on his stance on abortion. 

Both candidates have treated social media as a battlefield in which to attack their foes. Mr. Bolsonaro targeted Mr. da Silva for corruption while the left candidate called the president a “pedophile.” As a result, the Electoral Supreme Court prohibited the candidates’ teams from using social media to insult or defame their opponents. Some political analysts saw this as a restriction on freedom of expression.

Mr. da Silva was president of Brazil for two terms that were known for being economically strong. However, after 14 years with the Workers Party in power, Brazil ended with the worst recession on record, a corruption scandal, and the impeachment of Mr. da Silva’s handpicked successor, Dilma Rousseff.

Mr. Bolsonaro, on the other hand, faced a global pandemic, and the Russian-Ukraine war that debilitated the global economy. However, inflation in Brazil is now down for a third consecutive month, and unemployment rates have declined to 8.7 percent from 12.1 this time last year, the lowest level since 2015.

During the first round of elections, Brazilians also elected 27 out of 81 senators and all 513 members of the Chamber of Deputies. 

Mr. Bolsonaro’s party won 99 seats in the Chamber of Deputies, while Mr. da Silva’s won 80. Mr. Bolsonaro’s results were the highest for one party since 1998. For the senate, Mr. Bolsoanro’s party has 13 seats, as opposed to Mr. da Silva’s nine. Political observers now say that if elected Mr. da Silva will have a hard time governing with a conservative Congress.

The congressional votes “prove that Mr. Bolsonaro has a lot of support,” a professor of international relations at the Federal University of São Paulo, Regiane Nitsch Bressan, told the Sun. 

On Sunday, 12 out of 27 governors will also be elected, including in São Paulo, the most populated state. In the first round, Mr. Bolsonaro’s candidate, Tarcisio Gomes de Freitas, won 42 percent of the votes, while Mr. da Silva’s candidate, Fernando Haddad, who received 35 percent.