After a polarizing campaign, Brazil votes for its next president Sunday in a combative heavyweight bout threatening to test its young democracy: far-right incumbent Jair Bolsonaro versus leftist former leader Luiz Inacio Lula da Silva.
Lula, the charismatic but tarnished ex-metalworker who led Brazil through an economic boom from 2003 to 2010, leads in the polls, seeking to stage a stunning comeback four years after being jailed on controversial corruption convictions -- since annulled by the Supreme Court.
Bolsonaro, the pugnacious ex-army captain whose popularity has suffered from the carnage of Covid-19 and a sputtering economy, is gunning for a come-from-behind win and has strongly hinted he would not accept a loss.
He has repeatedly alleged, without evidence, that Brazil's electronic voting system is plagued by fraud.
Lula enters the home stretch leading Bolsonaro 50 percent to 36 percent, according to the latest poll from the Datafolha institute, released Thursday.
The figures, which exclude voters planning to cast blank or spoiled ballots, put Lula on the cusp of winning outright and avoiding a runoff on October 30.
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Lula is pulling out all the stops for a first-round victory, crisscrossing the country and summoning the star power and sex appeal of celebrity supporters like pop superstar Anitta and singer-songwriter Caetano Veloso to convince wavering Brazilians to cast a "tactical vote" for him.
"What's at stake is democracy versus fascism," the gravelly voiced 76-year-old told a cheering crowd decked out in the red of his Workers' Party (PT) at a rally last month.
It is a line heard often these days in the sprawling country of 214 million people, deeply divided after four years of Bolsonaro's social media polemics, anti-establishment attacks, disregard for deforestation in the Amazon and no-holds-barred battle on behalf of his "Bible, bullets and beef" coalition -- Evangelical Christians, security hardliners and the powerful agribusiness sector.
Leading mass marches and motorcycle rallies by supporters draped in the green and yellow of the flag, Bolsonaro has tapped the popularity of his telegenic, devoutly Christian first lady, Michelle, and got a high-voltage endorsement of his own Thursday from football superstar Neymar.
With Bolsonaro, 67, having vowed his re-election bid can only have three outcomes -- "prison, death or victory" -- the election could be turbulent for Latin America's biggest country, which emerged from two decades of military dictatorship in 1985.
"The stakes are huge... Democracy is on the ballot," said political analyst Michael Shifter of the Inter-American Dialogue think tank, calling Bolsonaro "the most anti-democratic president" since the military regime.
Some degree of unrest and violence "is probably likely," he told AFP.
The "million-dollar question" is exactly what shape this unrest would take, said Guilherme Casaroes, a political scientist at the Getulio Vargas Foundation.
Bolsonaro, who is openly nostalgic for the dictatorship, has given the military a big role in his government and enthusiastically courted its support.
But defense experts say an all-out military coup is unlikely.
A Bolsonaro court challenge or bid to delay the runoff election are stronger possibilities, analysts say.
More troubling is what Casaroes calls the "Capitol riot scenario": a Brazilian version of the turmoil unleashed by supporters of former US president Donald Trump -- Bolsonaro's political role model -- when he refused to accept electoral defeat.
Gun ownership has boomed under Bolsonaro's firearm-friendly policies: since he took office on January 1, 2019, the number of registered gun owners has more than quintupled to 673,000.
That, combined with die-hard support for Bolsonaro among some sectors of the military and police, is making observers nervous in Brazil and beyond.
The White House warned against violence Tuesday, saying the United States will be watching "closely."
Brazil's 156 million voters will also be electing the lower house of Congress, one-third of the Senate and governors and state legislators in all 27 states.
Polls open at 8:00 am and close at 5:00 pm (1100-2000 GMT), with results expected some two hours later.