This is the first KQED Political Breakdown/Change Research poll, which was conducted between Sept. 12-15 and asked 3,325 likely Democratic California primary voters who their top presidential choice was. The online survey has a margin of error of plus or minus 1.7%.
KQED is the exclusive media partner with Change Research, a San Francisco Bay Area-based polling firm whose paid candidate clients are primarily Democrats but who conduct polls in a nonpartisan manner. Polls will be conducted monthly through the March 2020 primary, and KQED will publish the results of each one. Read more about the polling process here.
This most recent poll shows a sharp decline in support for Harris since Change Research's last poll taken in July, when she was first among California Democratic primary voters with 23% support, trailed by Warren and Sanders, with 22% and 20% respectively.
Pat Reilly, co-founder of Change Research, said the survey results indicate that California Democrats are far from decided on their presidential preferences and that the race remains very fluid ahead of the March 3, 2020, primary.
"Californians are still evaluating the field," Reilly said. "And one candidate on top in a single survey months before an actual vote is cast is one data point in a campaign that's far from over."
Sanders is leading among voters ages 18-34, while Warren is the preferred candidate among voters ages 35-49 and 50-64. Biden and Warren are tied among voters 65 and older.
Harris, who is seeking to become first African American woman nominated for president by a major political party, has a slight lead over Biden among black voters, at 27% to 24%. Warren is a close third, with 21% black voter support.
Among Latino voters, Sanders has a 17-point lead over both Warren and Biden (35% to 18%).
Meanwhile, Warren is the first choice among white voters, with 31% support, followed by Sanders at 19% and Biden at 16%.
The third-quarter fundraising period, which ends Sept. 30, will provide a strong indication of how donors are judging the viability of these candidates. The next Democratic candidate debate will be held in mid-October in Ohio.
Charts produced by KQED's Matthew Green