Proposition 40, commonly referred to as the billionaire tax, came out of the gates hot.
Its proposal for a one-time, 5% tax on billionaire wealth for health care resonated with Californians, especially after federal cuts to health care by Congress and the Trump Administration. Sen. Bernie Sanders and Reps. Ro Khanna and Maxine Waters have endorsed and campaigned for the tax. As billionaire wealth continues to grow at an astronomical rate (170% since 2023), the tax has proved appealing, especially for young voters and Democrats, according to UC Berkeley polling and data from Forbes.
In March, a UC Berkeley Institute of Governmental Studies (IGS) poll found that yes votes held a 19-point lead, with 52% saying they support, 33% saying they oppose and 15% saying they are uncertain.
However, the ballot measure’s momentum has since declined. A Politico California and UC Berkeley's Citrin Center for Public Opinion Research poll released last week found that the lead has dropped to two percentage points, with 45% supporting and 43% opposing the tax. A new IGS poll that was also released last week found a similar three-point lead.
"A very common pattern is these initiatives start out with a lead," UC Berkeley Political Science Professor Emeritus Jack Citrin said. "They start out with a lead because the people who are for it are enthusiastic. They know what it's about. They're ready to say yes. There's a large segment of the electorate who doesn't really know much about it, and as they learn more about it, the campaign against it begins."
The campaign against the proposition has been spearheaded by Building a Better California, a political action committee backed by Google co-founder Sergey Brin. UC Berkeley Economics Professor Emmanuel Saez, whose research helped inspire Prop. 40, said billionaires have spent more than $200 million campaigning against the tax.
In comparison, supporters of Prop. 40 have spent $36 million, according to The Sacramento Bee.
"The fight around Prop. 40 has literally become a fight between democracy and oligarchy. If Prop. 40 wins, this will be a historical turning point showing that people can fight back against the growing power of billionaires, and is likely to be emulated in other states, the nation and other countries," said Saez, who is also director of UC Berkeley’s James M. and Cathleen D. Stone Center on Wealth and Income Inequality
Prop. 40 faces challenges on multiple fronts. Some, including Gov. Gavin Newsom, argue that it would cause billionaires to leave the state, creating a one-time revenue boost but costing the state taxes from billionaires in the long run.
"The one-time 5% wealth tax would be owed by any billionaire who was a resident of California on Jan. 1, 2026 — it is too late to move," said UC Berkeley and Paris School of Economics Professor Gabriel Zucman, whose wealth inequality research also inspired the wealth tax.
The California Teachers Association, California Professional Firefighters and California Police Chiefs Association oppose a billionaire wealth tax, according to Citrin, because they see the proposition as infringing on their availability to get funding, as the entire revenue generated by the tax is going to health care.
The Citrin-Politico poll revealed another facet of the tax: Californians think it will be recurring. Despite it claiming to be a one-time tax, 60% to 70% of respondents doubted that claim, the poll revealed.
The tax is one of the most contentious issues on the November ballot, with ramifications far and wide.
"It would also be the first-ever billionaire wealth tax enacted anywhere in the world, and as such, could represent a major turning point in global tax policy — paving the way for other states, the federal government and other countries to implement their own billionaire wealth tax," Zucman said in an email.
The Citrin-Politico poll also asked voters about two more topics: artificial intelligence and the 2028 presidential election. Despite not being a top priority for a vast majority of voters, anti-AI sentiment has spiked, with more than three-quarters of California voters responding that advanced AI is likely a threat to humans.
As for the 2028 presidential race, both Newsom and former Vice President Kamala Harris saw a decline in their support by more than 10 percentage points from March, though Newsom remains more popular.
"If you believe that a democracy should follow public opinion, then polling is one indicator of what public beliefs are about the policies of the day," Citrin said. "So while that's also a signal to the candidates, it's just a more general signal about what people believe policy should be."
