After a divisive campaign, Brazil on Sunday will elect its next president in a combative heavyweight battle that threatens to test its fledgling democracy: far-right incumbent Jair Bolsonaro versus left-wing former leader Luiz Inacio Lula da Silva.

Lula, the charismatic but ailing ex-metal worker who guided Brazil through an economic boom from 2003 to 2010, is leading the polls and attempting a stunning four years after his arrest on controversial corruption convictions – which have since been overturned by the Supreme Court to celebrate a comeback.

Bolsonaro, the quarrelsome ex-army captain whose popularity has suffered amid the carnage of Covid-19 and a faltering economy, is seeking victory from behind and has strongly indicated he would not accept defeat.

He has repeatedly claimed without evidence that Brazil’s electronic voting system is riddled with fraud.

Lula is entering the home stretch, leading Bolsonaro by 50 to 36 percent, according to the latest Datafolha Institute poll released on Thursday.

The numbers, which exclude voters who plan to cast blank or tainted ballots, put Lula on the cusp of winning outright and avoiding an Oct. 30 runoff.

Pulling out all the stops for a first-round win, Lula criss-crosses the country, summoning the star power and sex appeal of celebrity supporters like pop superstar Anitta and singer-songwriter Caetano Veloso to convince wavering Brazilians to use a “tactical voice.” to give him up.

“What’s at stake is democracy versus fascism,” the 76-year-old said huskily at a rally last month to a cheering crowd dressed in his Labor Party’s (PT) red.

It’s a phrase often heard these days in the sprawling country of 214 million, deeply divided after four years of Bolsonaro’s polemics on social media, attacks on the establishment, disregard for deforestation in the Amazon and relentless fight for his own is “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 into the popularity of his telegenic, devout Christian first lady Michelle, and received a high-voltage endorsement of his own Thursday from soccer superstar Neymar.

With 67-year-old Bolsonaro having only three outcomes after pledging his re-election – “prison, death or victory” – the election for Latin America’s largest country, which emerged from two decades of military dictatorship in 1985, could be a turbulent one.

“The stakes are high… Democracy is on the ballot,” said political scientist Michael Shifter of the think tank Inter-American Dialogue, calling Bolsonaro “the most anti-democratic president” since the military regime.

Some level of unrest and violence “is likely likely,” he told AFP.

The “million-dollar question” is exactly what form these riots would take, said Guilherme Casaroes, political scientist at the Getulio Vargas Foundation.

Bolsonaro, who is openly nostalgic for the dictatorship, has given the military a large role in his government and has enthusiastically enlisted its support.

But defense experts say a total military coup is unlikely.

A court challenge to Bolsonaro or an attempt to delay the runoff are stronger possibilities, analysts say.

Even more disturbing 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 an election defeat.

Gun ownership has boomed under Bolsonaro’s gun-friendly policies: since he took office on January 1, 2019, the number of registered gun owners has more than quintupled to 673,000.

That, coupled with the ingrained support for Bolsonaro from some sectors of the military and police, is making observers in Brazil and beyond nervous.

The White House on Tuesday warned of violence and said the United States was “watching closely.”

Brazil’s 156 million voters will also elect the lower house of Congress, a third of the Senate and governors and state representatives in all 27 states.

Polling stations open at 8:00 am and close at 5:00 pm (1100-2000 GMT). Results are expected about two hours later.