Will Brazil’s far-right make a push for a first-round win?

What a difference a week makes. Seven days ago, Workers’ Party candidate Fernando Haddad’s steep ascending trend gave pundits reason to believe that he would finish the first round ahead of frontrunner Jair Bolsonaro. On Sunday, a poll by MDA/CNT showed Mr. Haddad statistically tied with Mr. Bolsonaro. “I forecast that [Haddad] will finish the first round with 35 percent of valid votes,” said political scientist Alberto Carlos Almeida on Twitter.

Now, Mr. Haddad faces the possibility of the election not even reaching the runoff stage, as Mr. Bolsonaro makes a push for a first-round win. He currently stands at 39 percent of valid votes (discounting spoiled ballots), against the Workers’ Party’s 25 percent. While climbing 11 points in two days seems a lot, there is clearly a wave of support in favor of the far-right candidate.

His polling numbers have skyrocketed over the past month, going from 24 percent of total votes on September 10 to 35 percent on October 4. When we count only valid votes, Mr. Bolsonaro is at 39 percent. And the latter is the metric that counts the most, as candidates require over 50 percent of valid votes to win in the first round.

It may seem impossible for him to grow by 11 points in two days – however, it is anything but impossible. The gap to a Bolsonaro first-round win is not 11 points, but rather 5.5 points. As the...