Right-wing senator Flávio Bolsonaro has won the endorsement of Augusto Cury, who finished third in the first round of Brazil's presidential election, strengthening his bid to unseat incumbent leftist President Luiz Inácio Lula da Silva in the runoff on October 25. "My support is not a blank check," Cury said in a statement on Thursday. He took nearly 3 percent of the vote on Sunday, while Bolsonaro won 47 percent and Lula 45 percent.

Cury is the latest of several former rivals to line up behind Bolsonaro this week. Ronaldo Caiado, a former governor of Goiás state who won around 2.2 percent, endorsed him at an event in Goiânia, saying: "I'm here to defeat the PT", a reference to Lula's Workers' Party. Romeu Zema, a former governor of Minas Gerais, who took less than 1 percent, backed him on Monday. São Paulo governor Tarcísio de Freitas, re-elected on Sunday, also attended the Goiânia event. Renan Santos, the fourth-placed candidate with 2.6 million votes, has refused to back either contender.

A Datafolha poll published Thursday put Bolsonaro at 52 percent against 48 percent for Lula. Lula, 81, who is seeking a fourth term, played down the surveys. "I don't assess polls, I don't work like that," he said, adding that he has 17 days to win more votes than his rival. His campaign team has said he will seek direct confrontation in the runoff, and he is strengthening his presence on social media, where the right has traditionally had the upper hand.

Bolsonaro, 45, is the eldest son of far-right former president Jair Bolsonaro, who is serving a 27-year sentence for plotting a coup after losing the 2022 election and is under house arrest. The younger Bolsonaro has outlined an ambitious agenda: cutting the number of ministries, appointing at least four Supreme Federal Court justices, and pursuing a constitutional reform that would change the judiciary, lower the age of criminal responsibility from 18 to 16 and abolish presidential re-election. His remark that he would use his Liberal Party's legislative weight to "amend the Constitution, to redemocratise the country" caused concern, and he told critics fearing an authoritarian turn: "Let's come back down to the real world."

The proposal matters because of the arithmetic of Congress. A constitutional amendment needs three fifths of each chamber in two votes, or 308 of 513 deputies and 49 of 81 senators. According to El País, the Liberal Party won 121 seats in the lower house, 20 percent more than in 2022, and with allies would hold around 50 Senate seats. Thousands of people protested in São Paulo and other cities on Thursday, and in Rio de Janeiro a day earlier, against what they fear would be a return of the far right to power.