A knife-wielding man stabbed far-right congressman Jair Bolsonaro at a campaign rally on Thursday as he was being carried on the shoulders of a supporter. He suffered serious internal bleeding, according to surgeon Luiz Henrique Borsato, and underwent surgery in the small city where the attack happened.

Borsato said Bolsonaro was in serious but stable condition and would remain in intensive care for at least seven days. He was being transferred Friday to a premier hospital in Sao Paulo.

While it was unclear how long Bolsonaro would be unable to campaign, his vice presidential running mate, retired Gen. Hamilton Mourao, told reporters that the candidate will “come out of this process stronger than he went in.”

The candidate's son echoed that belief in a tweet:

“Jair Bolsonaro is stronger than ever and ready to be elected President of Brazil in the first ROUND!” Flavio Bolsonaro wrote. About a dozen candidates are competing in the Oct. 7 voting. If no one wins an outright majority, there will be a second round Oct. 28.

Bolsonaro, a former army captain who has promised to crack down on crime and corruption, has long argued that Brazil is in chaos and needs a strong hand. That message has resonated with many Brazilians, putting him in second place in polling, but his often derogatory comments about women, blacks and gays have also repulsed many.

In a video shot by a senator who visited him in the hospital, Bolsonaro thanked his medical team in a weak and scratchy voice and said: “I never did harm to anyone.”

The motive for the attack on Bolsonaro remained unclear.

“Our agents there said the attacker said he was 'on a mission from God,' ” Luis Boudens, president of the National Federation of Federal Police, told The Associated Press. “ Their impression is that they were not dealing with a mentally stable person.”

Federal police said that another suspect was detained in connection with the attack and questioned. That suspect was released overnight but remains under investigation.

Videos of the attack posted on social media show Bolsonaro on the shoulders of a supporter, looking out at the crowd and giving a thumbs-up with his left hand. He suddenly flinches and then goes out of view. Other videos show supporters carrying him to a car and hitting a man who was apparently the attacker.

The suspect, identified by authorities as 40-year-old Adelio Bispo de Oliveira, was arrested within seconds.

The attack shakes up what was already an unpredictable and contentious campaign. The man leading polls, former President Luiz Inacio Lula da Silva, has been barred from running by electoral authorities because he was convicted of corruption and is in jail.

Despite uncertainly over the motive, Brazilians surged onto social media to argue over whether the attack supports Bolsonaro's assertions that the country is off the rails or whether his heated rhetoric contributed to inciting the attack.

“They made Bolsonaro a martyr,” said Jonatan Valente, a student who joined a small vigil for Bolsonaro in Sao Paulo. “I think the left shot itself in the foot because with this attack they will end up electing Bolsonaro.”

After more than four years of revelations of widespread corruption within Brazil's political class, anger is running high in the country.

Bolsonaro, despite being a congressman since 1991, has harnessed much of the anger and presented himself as a maverick who will clean up a corrupt system. He also promises to confront a surge in crime, in part by giving police a freer hand to shoot and kill while on duty.

He speaks nostalgically about the country's 1964-1985 military dictatorship and has promised to fill his government with current and former military leaders. His vice presidential running mate is a retired general.

This is not the first time in recent months that violence has touched politicians. In March, while da Silva was campaigning in southern Brazil before his imprisonment, gunshots hit buses in his caravan, though no one was hurt. Also that month, Marielle Franco, a black councilwoman in Rio de Janeiro, was shot to death along with her driver.

“It's likely that Bolsonaro will use the attack to argue his opponents are desperate, that they had no other way to stop him,” said Mauricio Santoro, a political science professor at Rio de Janeiro's state university.

Mauricio Savarese and Sarah DiLorenzo report for the Associated Press.