President Jair Bolsonaro, having denied President Luiz Inácio Lula da Silva a majority in the first round of Brazil’s presidential election, has at least a chance of prevailing in a run-off at the end of the month, and has already won an upper hand in the Congress. 

Mr. da Silva, who was in office as president between 2003 and 2010,  led the results of the voting Sunday with 48 percent. Mr. Bolsonaro received 43.5 percent, finishing with a tighter outcome than the polls predicted. The runoff is shaping up as a historic contest.