Neither President Luiz Inácio Lula da Silva nor Flávio Bolsonaro, the son of a former president, won the first round, but Mr. Bolsonaro took more votes.
President Trump is doggedly lending his support to Republican candidates facing a rough midterm season. He is the same campaigner he has always been, but his crowds have changed.
Luiz Inácio Lula da Silva, the leftist incumbent, and Flávio Bolsonaro, the right-wing challenger, face off in a race that could define the future of Latin America.