A tally kept by the investigative journalism group Agência Pública tracked more than 70 attacks in the first 10 days of October. While most of the reports involve attackers who appeared to support Mr. Bolsonaro, six of his backers have also said they were targeted.

This surge of political violence comes at a time when Brazil’s murder rate has hit a record high. Mr. Bolsonaro’s radical tough-on-crime message has resonated with a population furious over the escalation of crime and fed up with political corruption and the painful effects of a deep recession.

But many critics believe Mr. Bolsonaro’s inflammatory rhetoric is in part responsible for stoking this climate of violence against political opponents. He often says that “violence should be fought with violence,” and mimics the firing of a pistol with his hands during speeches.

During a recent campaign rally in the northern state of Acre, he hoisted a tripod, pretended it was a machine gun and told supporters, “Let’s shoot Acre’s Workers’ Party supporters,” in a reference to the leftist party whose candidate, Fernando Haddad, he faces in the runoff on Oct. 28.

Mr. Bolsonaro’s campaign later said he was joking.

He has also vowed to make it easier for citizens to own guns and, in a country where police violence has long been a problem — over 5,000 people were killed by police officers in 2017 — he promised to give the police license to kill suspected criminals. One of the candidate’s sons posted on Twitter a photo that simulated the torture of an opponent.