Insults traded on social media and a combative debate have intensified the pressure ahead of a fiercely contested presidential run-off on Sunday, with only a few points separating leftist pro-union President Luiz Inacio Lula da Silva and far-right challenger Flavio Bolsonaro, the son of former president and Trump ally Jair Bolsonaro.

The final stretch of the election campaign is under way in Brazil as President Luiz Inacio Lula da Silva (L) faces far-right challenger Flavio Bolsonaro. © AP et Studio graphique FMM With music blaring, parade floats and glitter in the colours of the Brazilian flag, several hundred supporters rallied in street-carnival style on Wednesday in the working-class neighbourhood of Bangu, in western Rio, to support right-wing presidential candidate Flavio Bolsonaro In the heart of the Vidigal favela some 40 kilometres (25 miles) away, a few dozen members of President Luiz Inacio Lula da Silva 's Workers’ Party were rallying the troops by handing out flyers to the last undecided voters.

But in both Bangu and Vidigal, the festive spirit is gone. Both camps mobilise their 'armies' Since the extremely close first-round results were announced on October 4, war has been declared between the two candidates. The self-proclaimed “Commander-in-Chief of the President”, MP André Janones of Minas Gerais, has created “Lula’s army” – a WhatsApp channel that garnered more than 8 million followers in just a few days. The channel aims to mobilise activists and anti- Bolsonaristas by issuing them challenges on social media or in the streets.

Surprised at not having won the first round, Lula has handed over control of his campaign to the younger generation of elected party officials. These digital soldiers have re-energised his campaign, which was criticised for its inertia before the first round. But it may be too little, too late. “This is the least-organised campaign I have taken part in since 1989, and we reap what we sow,” the president admitted in a meeting with allied lawmakers.

The octogenarian president has recently begun filming himself, always accompanied by activists under 30. The goal is to win over young non-voters, some 6.9 million Brazilians – only a fraction of those would have been enough to tip the election. For Josue Medeiros, coordinator of the Political and Electoral Observatory at the Federal University of Rio de Janeiro, this digital awakening could make the difference. “The number of undecided voters has risen, to between 7 and 14%, and that is a good sign for whoever came second in the first round, because these are people who are wavering and could change their vote. It means this digital mobilisation is working; it creates doubt and reduces the sense that President Lula was being rejected, which was very strong before the first round.”

The Bolsonarist camp, for its part, is not sitting on its hands. Facing Lula’s army, Flavio has unleashed his own “troops”, led by young MP Nikolas Ferreira, who can activate his 25 million followers on demand. Their specialty? Using AI-generated content to disparage left-wing rallies.

The digital battle has also moved into the courts. Accused of favouring the right-wing candidate, Lula’s camp denounced Meta for “algorithmic manipulation” in Bolsonaro's favour and asked the Superior Electoral Court to annul the challenger's candidacy. Bolsonaro, in turn, accused the incumbent of “abuse of power” for flooding WhatsApp with content praising his government’s record. Under pressure from the high court, which threatened the company with a fine of around R$500,000 (€88,500) per day, Meta now says it has put measures in place to guarantee equal treatment of both candidates.

Polls tighten Having come out ahead in the first round with about 47% of the vote against 45% for Lula, Bolsonaro seemed to have the momentum: an October 9 AtlasIntel poll credited him with 52.8% of the vote to Lula's 47.2%. Ten days later, the same firm had him at only 51.1% against 48.9% for the incumbent president while other pollsters (Datafolha, Quaest, CNT/MDA) showed a gap of just one or two points between the candidates. In the meantime, Lula won a major victory in Congress: a vote to end the six-day work week.

The overwhelming approval of this measure by the Senate (75 votes to 1) made this labour-law reform a strategic victory as the run-off approached. Initially opposed to the measure, the Bolsonarist camp ended up voting in favour. The left now warns that Bolsonaro will reverse the law if elected, given that he has been a staunch ally of business owners and agribusiness, which fiercely opposed the law. “It is important to remember that our opponents decided yesterday to vote for this measure. But let’s stay vigilant! They voted for it out of electoral opportunism,” Lula said in a video posted on his Instagram account.

xiety-provoking debate Amid repeated charges of opportunism and lying, the tone of the run-off had turned tense even before reaching a fever pitch in the first debate between the two candidates on October 18. The face-off was highly anticipated, particularly after Lula refused to debate his opponent ahead of the first round.

contentious debate of nearly two hours live on the Band channel held the attention of some 158 million Brazilian voters. But little detail emerged on the candidates' respective platforms regarding security, health or the economy – instead there was an avalanche of insults and jabs, often referencing the allegations of corruption tainting both parties.

The debate was meant to convince the 33 million abstainers to vote on October 25. But according to Joao Ferres, political scientist at the University of Rio de Janeiro, “debates are watched less and less by Brazilians and do not influence voting intentions much. This confrontation mostly hurt Flavio Bolsonaro, who came across as aggressive; Brazilian voters don’t like that kind of behaviour.”

The electric atmosphere sent deputy Andre Janones to intensive care shortly after the debate with severe cardiac arrhythmia triggered by stress and fatigue He was not the only one to have suffered aftereffects, with some viewers reporting symptoms of " political anxiety " including cold sweats, panic attacks, irritability or insomnia.

A few days after the debate, Bolsonaro relented and agreed, with conditions to accept Lula's challenge to make their banking, tax and phone records public.

Verdict at the ballot box Progressive independent media outlet Brasil fora da Caverna recommended voting early on Instagram: “Go vote before noon on Sunday, October 25, because afterward we don’t know what might happen.”Lula’s supporters are also urging voters to go to the polls as early as possible: “In case of transport problems, a change of polling station, queues or any other unforeseen event, you will still have time to find a solution and exercise your right to vote,” his team posted on In an election that is widely expected to be decided by just a few points, every vote is going to count.