Datafolha, a prominent pollster in Brazil, published the last major Brazilian presidential election poll expected before this weekend on Thursday, finding a sizable, though diminished, lead for conservative Jair Bolsonaro over socialist candidate Fernando Haddad.

Brazilians will vote in the second and final round of their presidential election on Sunday. Bolsonaro defeated Haddad and several other candidates in the first round of voting this month but did not reach the 50 percent threshold necessary to prevent a run-off vote with the second most popular candidate.

In Thursday’s poll, Datafolha found that Bolsonaro, of the conservative Social Liberal Party (PSL), leads the Workers’ Party (PT) Haddad with 56 percent of the vote. Haddad received the support of 44 percent of respondents, while the rest were undecided or choosing to cast a blank ballot (Brazil has compulsory voting laws). The 12-percent lead is significantly smaller than the 14-percent lead competing polling firm Ibope found for Bolsonaro this week, but still far larger than the two-percent margin of error in Datafolha’s survey.

The poll found 14 percent of people are either not voting for either candidate (casting blank votes) or undecided. This number is larger than the gap between the two candidates for the first time since the first round of voting. As blank ballots are not necessarily undecided voters, however, there is no guarantee that these voters will choose one side or the other; on the contrary, it is possible that those who claimed to be supporting either Bolsonaro or Haddad will change their vote to a blank ballot by Sunday.

The Brazilian newspaper O Globo notes that it does appear that Bolsonaro’s momentum has marginally stalled. The drop is larger when comparing the latest Datafolha poll to the most recent previous one, which found Bolsonaro 18 points ahead. Haddad also gained support, particularly among the nation’s wealthiest voters.

The general director of Datafolha, Marcos Paulino, told O Globo that he believes the narrowing is part of a “return” by traditional PT voters to their party. “There is a wing of Bolsonaro’s supporters who came from the PT … these may be coming home due to the events of this past week,” Paulino suggested.

The head of Ibope, Carlos Augusto Montenegro, also made public remarks on Thursday, suggesting that, at this point, it was nearly impossible for Bolsonaro to lose.

“The big question is by how much [Haddad] will lose,” Montenegro said in an interview with Estadão. “Certainty [percentages] among voters of the two [are] very large and both sides are antagonistic. Only a tsunami could make a Haddad voter into a Bolsonaro voter and vice versa.”

The socialist PT has governed the country for most of the 21st century, ending their reign only upon the impeachment of President Dilma Rousseff in 2016. Since then, current President Michel Temer, of the non-ideological Brazilian Democratic Movement Party (PMDB), has largely attempted to keep a low profile as he awaited his departure from the job. During Rousseff’s tenure, local officials in Curitiba, a southern city, found evidence of local corruption that began the probe now known as “Operation Car Wash,” in which officials from almost all of Brazil’s political parties were found to be taking kickbacks from private corporations to secure infrastructure contracts. While Rousseff herself has not been found guilty of any crime, her predecessor, PT leader Luiz Inácio Lula da Silva, was sentenced to 12 years in prison for buying a luxury beachfront property with “Car Wash” money. Delivering what could be a death blow to the PT, Lula refused to withdraw his nomination to the presidency until September despite being legally ineligible to be president. Haddad has thus had little less than two months to campaign.

On the other side of the ballot, Bolsonaro has no public record of corruption, but cultivated a polarizing public image for years, attacking leftists by lamenting that the Brazilian military dictatorship of the past century did not kill enough of them and refusing to condemn Chilean dictator Augusto Pinochet. Bolsonaro significantly tempered his language during the campaign, however, instead focusing on eradicating corruption from the country, fighting crime, cutting ties to leftist governments like China and Venezuela, and expanding individual gun rights.

Bolsonaro’s campaign was hurt in September by a significant assassination attempt, a stabbing that left him in hospitalized for weeks and required partial reconstruction of his intestinal tract. The culprit was identified as a longtime socialist who told police he was “sent by God” to kill Bolsonaro.

Bolsonaro’s campaign was most recently hurt by a Facebook crackdown that shut down dozens of accounts and pages supporters used to spread the word about his policies – particularly important given that Bolsonaro’s recovery from the stabbing limited campaign trail obligation.

Team Bolsonaro argued this week that they also face a challenge from Datafolha itself, despite the wide lead the current poll showed for their candidate.

“We still do not believe the research, especially Datafolha,” presidential committee chairman Gustavo Bebianno reportedly said on Friday. “Datafolha is part of the Folha network and we do not believe in the Folha network or the Datafolha research institute. The top Brazilian newspaper producing fake news – it’s a shame,” Bebianno said.

Folha de Sao Paulo is one of Brazil’s largest newspapers and affiliated with Datafolha. Its coverage tends to skew left.

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