The University of Southern California’s Democracy and Fair Elections Lab found Wiener with 47% support and Chan with 41%; 9% of respondents were undecided. The survey was conducted Oct. 16-19, less than two weeks before the Nov. 3 election, and has a margin of error of plus or minus 4.6 percentage points. The lead is therefore within the poll’s margin of error.

Pelosi, who has represented the district for nearly four decades, endorsed Chan last spring and has campaigned for her. But the survey indicates that Pelosi’s popularity has not translated into unified support for her chosen successor: even among voters who view Pelosi favorably, Wiener has a slight edge.

Christian Grose, a USC political science professor who led the poll, said the candidates draw support from different parts of the electorate. Chan is strongest among voters who identify as very liberal, Democratic Socialists of America supporters, independents and people with lower incomes. Wiener does better among voters who identify strictly as Democrats and those earning more than $100,000 a year.

The divide reflects the candidates’ contrasting political coalitions. Wiener, a state senator, has emphasized his record on pro-housing legislation. Chan, a progressive aligned with labor unions and liberal activists, has argued that Wiener is too close to business interests. Both candidates have ties to organized labor.

Grose said voters who are more likely to turn out in a midterm election appear to favor Wiener, while Chan’s strongest support comes from very progressive voters. He cautioned that the poll does not rule out a Chan victory, while saying its results favor Wiener.

The survey questioned 454 likely voters by email in English, Chinese, Spanish, Korean and Vietnamese. It is the only independent poll released in the race, according to the poll’s report.