He is vulgar and uncouth, and he recently sparked uproar for joking that he should have had the first turn at an Australian raped repeatedly and brutally killed during a prison riot in the southern Philippine city of Davao 27 years ago.

He has insulted Pope Francis, describes himself unapologetically as a "womaniser" and advocates vigilante killings of suspected criminals.

But none of this seems to matter.

Mr Rodrigo Duterte, the 71-year-old mayor of Davao who styles himself as a no-nonsense crime-fighter may well become the Philippines' next president when more than 55 million Filipinos vote in two weeks. He padded his lead in a survey released yesterday by polling firm Pulse Asia on whom Filipinos want to lead them for the next six years. He chalked up 34 per cent compared to 22 per cent for his nearest rival, Senator Grace Poe. But the survey was undertaken before the "rape joke".

During a prison riot in 1989, inmates held hostage 36-year-old Australian missionary Jacqueline Hamill. She was raped repeatedly and her throat slit.

Recalling the crime, Mr Duterte said at a campaign rally on April 12: "They lined up and raped her. I was angry because she was raped. That's one thing. But she was so beautiful. The mayor should have been first."

Faced with a torrent of criticism, Mr Duterte later apologised, saying in a statement: "Sometimes my mouth can get the better of me."

Pundits agree that this episode will likely pull down Mr Duterte's polling numbers, but whether it could cost him the presidency is anyone's guess.

Pulse Asia director Ana Tabunda said the rape joke had not been a factor in the April 12-17 survey as news about it began to surface only on April 18.

But she said it may not hit as hard as when Mr Duterte cursed Pope Francis for the heavy traffic caused by the pontiff's visit to the Philippines in January last year. "The rape joke is not as clearly wrong as cursing the Pope" to Filipinos, she said.

It is the image he has been cultivating since he was a street-smart thug in his teens, as well as the widespread discontent among the poor and the lower middle class, that is insulating Mr Duterte, analysts say.

Personalities trump issues in Philippine politics, and the narrative that resonates best with Filipinos is a back story that runs like a B-movie plot: The street rascal who has a heart of gold for the downtrodden, who with his wit, fists and excellent marksmanship decimates a wealthy, greedy and oppressive clique.

For his millions of supporters, Mr Duterte fits the bill.

A ladies' man, he was married to a flight attendant, Ms Elizabeth Zimmerman, for 27 years. They have three children, all adults and already carving their own careers in politics. He has an 11-year-old daughter with his current partner, Ms Honeylet Avencena, a nurse.

Along the way, he has gained the reputation of someone who can get the job done, by whatever means. By that token, he is seen as the candidate who can shake up the establishment and bring real change.

Mr Duterte prosecuted a brutal war on crime in Davao, once known as the Philippines' "murder capital", when he became mayor in 1988. The body count in that campaign was at least 1,000, and Mr Duterte has admitted to having a hand in a couple of death squad-style executions.

But the mass killings in Davao have not ended under his rule.

His defenders are quick to explain away his wicked tongue and his total disregard for civility and political correctness as simply the habits of a straight-shooting, unpretentious man - a sharp contrast to the smooth-talking politician favoured by the upper class.

"The masses are not shocked by Duterte's gutter language because that's also the language they speak," said Mr Ramon Tulfo, the Philippine Daily Inquirer's self-styled "tough guy" columnist.

It is, in fact, the gutter language that whips the crowd into a frenzy, according to popular blogger Ellen Tordesillas.

"People are delighted whenever he shouts obscenities on stage because they get this feeling that they themselves are finally getting the chance to vent their anger at criminals, drug dealers and corrupt government officials," she said.

But for De La Salle University political analyst Richard Javad Heydarian, Mr Duterte's rise marks "a race to the bottom".

If Mr Duterte survives the rape-joke brouhaha, he may well become the next president. But already his opponents have been upping the attacks. A medical report saying Mr Duterte suffers from "anti-social narcissistic personality disorder" has surfaced.

For now, though, Mr Duterte remains the man to beat on May 9, and he is promising that if he wins, "God himself will weep".