Supporters of Jair Bolsonaro, the far-right Brazilian presidential candidate who was stabbed during a recent campaign event, rally around an inflatable likeness of him in Sao Paulo on Sept. 9. His condition is serious but stable. (Andre Penner/AP)

Presidential campaigning has begun in Brazil. In a country where voting is compulsory, about 140 million are expected to cast ballots on Oct. 7.

This presidential election is uniquely uncertain. The country’s most popular politician — former president Luiz Inácio Lula da Silva, known as “Lula” — is in jail for corruption and barred from the ballot. The mainstream parties and politicians are tainted by the same massive corruption investigation that brought down Lula — leaving a relatively open field.

This uncertainty means women’s votes may decide the election. Let me explain.

Brazil’s shaky political landscape

With Lula off the ballot, his leftist Workers’ Party put former Sao Paulo mayor Fernando Haddad — who was Lula’s candidate for vice president — on the ballot for the presidency. While being placed on the ballot gave Haddad a slight popularity boost, he’s still polling in the single digits. After “Operation Car Wash,” the corruption investigation, most mainstream parties’ candidates are down there with him.

So, who’s not? The leading contender to the presidency is right-wing congressman Jair Bolsonaro, a former colonel favored by 24 percent of Brazilians in the latest polling. The candidate was stabbed in the abdomen during a campaign event and has undergone surgery for an intestinal-tract injury. His condition is serious but stable; no one knows whether he’ll be able to campaign before the election. The attack has neither hurt nor improved his support, according to one of the first polls to come out since he was stabbed.

Brazil’s presidential polling shows an unprecedented gender gap, and a startling proportion of women haven’t decided at all.

Here’s where we get to the women’s vote. The attack definitely didn’t change the unprecedented Brazilian gender gap in candidate choice. Women are strongly against Bolsonaro, with nearly half saying they would not vote for him.

The former colonel is a divisive figure in Brazilian politics. He champions mostly right-wing, conservative, pro-gun, anti-LGBT policies. His campaign language is strongly tinged with misogyny, xenophobia, racism. As a result, observers often compare his ideas and style to that of President Trump, but also to Filipino President Rodrigo Duterte and to French presidential candidate Marine Le Pen.

Bolsonaro has also made several public remarks insulting women. On camera, he told a fellow congresswoman — who was accusing him of promoting rape culture — that he wouldn’t rape her “because she didn’t deserve it.” He once “jokingly” said that after having four sons, he “faltered” and had a daughter. Asked what he would do about the gender wage gap in Brazil, he has repeatedly answered with some version of “it is up to the market to decide,” essentially saying he will do nothing.

Female voters have noticed. When asked to state their preferred candidate, an average of 20 percent of those who were interviewed named Bolsonaro. When the number is broken down by gender, the difference is stark. While 28 percent of men named Bolsonaro, only 13 percent of women did the same.

While voters who said they hadn’t decided made up 37 percent of the sample, only 26 percent of men gave that response, while 46 percent of women did. Meanwhile, 14 percent of women and only 11 percent of men answered that they support no one. Add that up, and we see that close to 60 percent of Brazil’s female voters have not chosen a candidate.

The same poll also offered interviewees a list of all candidates, to see whether it changed their answers. With that prompt, Bolsonaro still leads with 24 percent, while three other candidates came next in a statistical draw of around 14 percent. Here again, Bolsonaro’s support divides by gender, with 32 percent of men supporting him and only 17 percent of women.

Perhaps his biggest hurdle is his rejection rate. When asked “for whom would you not vote?” with the option of rejecting more than one candidate, Bolsonaro leads with a total of 43 percent — rejected by 37 percent of men and 49 percent of women.

Brazil’s first round of voting will almost certainly lead to a runoff — and women’s votes will matter a great deal.

In absolute numbers, Brazilian female voters outnumber men by close to 7 million — with 76.5 million women over the voting age of 16 and only 69.7 million men. No candidate is expected to win more than 50 percent of the votes in the first round, which would be required to win outright. Even if Bolsonaro reaches the runoff, he can’t win unless he attracts more female voters before the final vote in late October.

So far, the only way Bolsonaro might win is if he’s competing against the Workers’ Party candidate, Haddad. In polling, 44 percent of women say they would support the leftist candidate in a runoff, and only 30 percent say they’d support Bolsonaro; men would swing the opposite way, with 34 percent saying they’d choose Haddad and 47 percent naming Bolsonaro.

Of course, a lot could change between now and then. Among other wild cards, between 20 and 25 percent of women did not know for whom they would vote, a bloc large enough to change the outcome.

While many things can happen, one thing comes close to certain: Women are poised to be the election’s key voters.

Deborah B.L. Farias is a lecturer at the University of New South Wales.