The contest follows an Oct. 4 first round in which Flávio Bolsonaro finished ahead of Lula. Recent polls put the candidates close, with some showing Bolsonaro leading and others showing the gap narrowing. One survey released Wednesday found that 10% of voters remained open to changing their minds.

A win would give Lula a fourth, nonconsecutive term. He has said this will be his final presidential campaign. A former union leader, Lula first took office in 2003 and later lost support amid a corruption scandal. He was jailed, but his convictions were subsequently annulled on procedural grounds.

The younger Bolsonaro has pledged to pardon his father, who is under house arrest while serving a 27-year sentence for plotting to overturn the 2022 election, which he lost to Lula. Flávio Bolsonaro has also proposed reducing the size of the state to encourage economic growth and has promised a forceful campaign against organized crime.

Crime is a central concern for some voters. “Security is awful,” said Marli Alves, a 63-year-old prison worker in Rio de Janeiro who supports Bolsonaro. She described robberies at outdoor events as a frequent fear.

Lula has challenged Bolsonaro’s economic ideas, including his praise for Argentine President Javier Milei’s austerity policies. In a televised debate, Lula pointed to rising poverty in Argentina and questioned whether Brazil should follow that model.

The candidates’ supporters have filled rallies in major cities and gathered at plazas and university campuses across the country. Camila Sixel, a 40-year-old corporate event planner campaigning for Lula in Rio, said Bolsonaro’s first-place finish in the opening round heightened her sense of urgency. She cited concerns about women’s rights, racism, inequality and protections for vulnerable people.

A Bolsonaro victory would extend his family’s influence over Brazil’s political right, which has increasingly moved beyond its previously more moderate leadership. Flávio Bolsonaro is also a close ally of U.S. President Donald Trump; his election would add to a broader shift toward conservative leadership in Latin America.

The campaign has also raised questions about political content on social media. Lula’s campaign accused Meta of unfairly restricting his material, a charge the company denied. Meta acknowledged technical problems in handling election-related content in Brazil, while saying it does not suppress or favor either side. The company’s content decisions and voter turnout could matter in a race expected to be decided narrowly.