A proposed tax on billionaires remains short of majority support as Californians begin casting ballots, according to a new Citrin-POLITICO poll.

Likely voters are essentially where they were a month ago, the survey found, with 46% in favor of Proposition 40 and 43% opposed — despite a recent push by backers of the measure, including Sen. Bernie Sanders, to rally support for the one-time, 5% tax on billionaires’ assets.

Sitting below a majority this late in a campaign is a red flag, according to ballot initiative veterans, and the static support reflects how difficult it has been for proponents to convert anti-billionaire sentiment into likely votes, said Jon Cohen, founder and CEO of TrueDot, whose firm fielded the poll.

“Californians do think billionaires should pay more,” Cohen said, but “it doesn't translate so easily into them voting for this tax.”Time is running short for supporters, led by health care union SEIU-UHW, as they contend with middling poll numbers and a staggering financial deficit against billionaires who have spent hundreds of millions of dollars to block the tax.

That lopsided advantage has allowed opponents to monopolize the airwaves, where they have warned the tax could be expanded. The tax’s proponents insist that is false, and pushing an additional tax through the Legislature would face daunting political and legal hurdles.

But the argument resonates with registered voters: Two-thirds doubted it would be a one-time tax, and the opponents’ most effective message was the claim that lawmakers could later expand it to cover people who aren’t billionaires, according to the poll.

Still, the survey suggested there are diminishing returns to the opposition onslaught. A strikingly high share of registered voters (84%) said they’d been exposed to s or messages about the tax, but a 45% plurality said the communications had not swayed them, and those whose views had shifted were just as likely to be more opposed as more supportive.

Lacking the resources to mount a serious television advertising campaign, supporters are counting on the inherent appeal of a populist message amplified by progressive champions like Sanders.

Registered voters are receptive to some of the tax campaign’s core messages, the poll finds: Comfortable 58% majorities said they were persuaded by the idea that billionaires can afford to pay more and that Prop 40 would furnish revenue for health care. And registered voters overall were far more likely to say billionaires should pay more (48%) than they were to say billionaires are valuable contributors whom California should avoid driving away.

In another positive sign for proponents, undecided likely voters were far more inclined to support Prop 40 (69%) than to oppose it (14%). Voters under 44 were notably more likely than their elders to back the tax, although younger voters tend to have lower turnout rates.

“This anti-billionaire hostility to the ultra rich and the belief that they should pay more is strong, very strong and hasn't really been eroded among those people who started out with a pro 40 (stance),” said Jack Citrin, a University of California, Berkeley, political science professor and co-director of the UC Berkeley Citrin Center for Public Opinion Research-POLITICO poll.

The people paying closest attention to California politics believe we’re headed for a tight finish. A concurrent survey of POLITICO’s audience of key political and policy influencers in the state — including political staffers, lobbyists, policy advisers and others deeply versed in California’s political landscape — found that plugged-in group was markedly more likely to call the measure too close to call: a 40% plurality of influentials said they didn’t know how Prop 40 would finish, compared to just a quarter of likely voters.

These data come from parallel surveys of California voters and policy influencers, fielded by TrueDot, the AI-accelerated research platform, in collaboration with the Citrin Center at UC Berkeley and POLITICO. Interviews for the voter survey were conducted online in English and Spanish from Oct. 9-14, among a sample of 1,149 registered voters, including 909 likely voters, selected at random through Verasight, with supplemental online panel recruitment. Voter results were weighted to California registered-voter benchmarks for age, educational attainment, race and ethnicity, gender, and geography, with additional calibration to 2024 presidential vote by region.

From Oct. 14-16, a parallel study was conducted in partnership with POLITICO among its audience of key political and policy influencers in California. The audience was defined based on job title and organizational affiliation and included state and local government employees, political staffers, lobbyists, policy advisers, consultants, business decision-makers and subject matter experts.

The margin of error is plus or minus 3.2% for the registered voter sample and plus or minus 3.6% for likely voters. The influencer survey has no calculable error margin.