California’s proposed billionaire tax appeared headed for defeat as ballot counting continued, potentially blocking a one-time levy on qualifying California billionaires.

Proposition 40 was trailing with about 54% of voters rejecting it and 46% in favor as of Friday, Nov. 6, with votes still being counted, the Los Angeles Times reported. The measure would have taxed roughly 200 California billionaires and raised an estimated $100 billion, mostly for healthcare.

The Beverly Hills Chamber of Commerce and the West Hollywood-Beverly Hills Democratic Club both opposed the measure, according to the Beverly Press. Gov. Gavin Newsom, incoming Gov. Xavier Becerra, the teachers union and Planned Parenthood also lined up against it.

The opposition campaign dwarfed supporters' spending. Opponents raised $316.7 million, while backers raised $34.3 million, nearly all from the healthcare workers union SEIU-United Healthcare Workers West, which crafted the measure, the Los Angeles Times reported. Google co-founder Sergey Brin donated more than $100 million to anti-Prop. 40 efforts. Former Google leader Eric Schmidt and venture capitalist L. John Doerr each contributed $40 million.

The four richest Californians — Brin, Nvidia CEO Jensen Huang, Google co-founder Larry Page and Meta CEO Mark Zuckerberg — would have owed 40% of the estimated taxes collected under the measure, according to a separate Los Angeles Times analysis.

Dan Schnur, a politics and communications professor at USC, UC Berkeley and Pepperdine University, told the Los Angeles Times the measure's ambition may have been its undoing.

"In a deep blue state like California, most voters are going to support additional funding for healthcare, especially to replace Trump funding cuts," Schnur said. "But in retrospect, the sponsors may wish they've been a little bit less ambitious."

Support had eroded steadily. A UC Berkeley Institute of Governmental Studies poll co-sponsored by the Los Angeles Times showed voter support fell to 42% from 52% in March. The concept of taxing assets rather than income unsettled even non-billionaire voters, the Los Angeles Times reported.

The opposition also extended beyond money. Two competing ballot measures, Propositions 41 and 42, were designed to block the wealth tax even if it passed. Proposition 42, which would ban new taxes on personal property such as stocks and artwork, was leading with 54.3% support in early returns, the Beverly Press reported. Newsom endorsed that measure.

Newsom opposed the state-level tax over concerns that wealthy residents would leave California. "Wealth is movable, and it shops for the state with the lowest taxes," Newsom wrote in June, according to the Beverly Press. "The fight belongs at the federal level, where this broken system was created in the first place."

The state's nonpartisan Legislative Analyst's Office had estimated the measure could eventually reduce state revenues by about $1 billion annually if wealthy residents left, NBC Los Angeles reported.

The fight may not be over. Suzanne Jimenez, chief of staff for SEIU-UHW, said the union would "pursue every available avenue, up to and including returning to the ballot in 2028 with a billionaire tax" if Sacramento does not find other ways to fund healthcare, the Los Angeles Times reported.

Election officials will continue counting ballots before certifying the results.