For most of his career, Sergey Brin kept his distance from politics. He once dismissed government as a "giant bonfire of partisanship."
A one-time donor to Barack Obama, the Google co-founder described Donald Trump's 2016 election as "deeply offensive" to him as an immigrant. A decade later, Brin has moved closer to the Republican Party, donated to Steve Hilton's campaign for California governor and joined the Trump White House's tech council.
Now, Brin is taking a more direct role in politics. He has committed more than $100 million to defeat a California ballot measure that would impose a one-time tax on billionaires' wealth, making him the largest individual donor to a ballot-measure campaign in state history.
A tax on billionaires' fortunes has been a signature idea of Senator Bernie Sanders, the Vermont independent, since his 2020 presidential campaign. He has called Proposition 40 the "most important ballot measure in America."
The campaign comes after Brin changed his residency to Nevada, where his representatives now say he lives. In December 2025, the Google co-founder registered to vote there, according to state records reported by Forbes. He had bought a $42 million home on the Nevada side of Lake Tahoe.
The target is Proposition 40, which is not a long-term wealth tax like the one Sanders and some other progressives have long championed. Instead, this measure would impose a one-time, 5 percent tax on the wealth of billionaires who lived in California on January 1, 2026.
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Bloomberg estimated the measure could cost Brin about $13 billion. His Nevada voter registration came three weeks before the cutoff.
Brin's spending has coincided with a tightening race, with recent polls showing the tax measure's once-comfortable lead narrowing to a statistical tie less than two weeks before the November 3 election. The fight has divided California Democrats, with Governor Gavin Newsom opposing a measure backed by others in his party. It has also turned the vote into a national test of whether a wealth tax can pass in one of the country's most Democratic states.
Supporters argue the campaign has beaten the odds before. "A handful of the most controversial billionaires in the state and their consultants spread misinformation and rumors that Prop 40 wouldn't make the ballot – it did," Suzanne Jimenez, chief of staff of Fwest and the measure's lead sponsor, said in a statement to Newsweek.
Jimenez accused Brin and other billionaires of spending more than $1 million a day to push voters toward the "poison pill" countermeasures. "The billionaires can buy all the ads they want," she said, but they "can't buy California voters."
Newsweek reached out to Brin, through Building a Better California, the committee he funds, and to the offices of Newsom and Representative Ro Khanna for comment.
Can Brin Escape the Tax?
One of the law professors who wrote the measure says Brin's move may not save him. "The purported 'move' was never very plausible," Darien Shanske, a tax law professor at UC Davis and one of the measure's drafters, told Newsweek.
Shanske pointed to a 2021 ruling by California's Office of Tax Appeals in a case known as Bracamonte. In early 2008, a couple from Escondido rented an apartment in Henderson, Nevada, registered to vote there, got Nevada driver's licenses and opened Nevada bank accounts. Months later, they sold their aviation business for nearly $17 million and argued they owed California nothing.
California's tax appeals judges ruled the couple were still residents on the day of the sale. They had kept their California home and most of their belongings, and between late February and July they spent 90 days in California against 28 in Nevada.
"As this case shows, the FTB would, if necessary, conduct a residency audit and Mr. Brin's continued engagement with his California businesses would make it even more likely he would be found to be a California resident," Shanske told Newsweek, referring to the state's Franchise Tax Board.
The New York Times has reported that Brin still spends every other week at Google's headquarters in California.
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"The CBTA piggybacks on 100 year old Ca residency law relating to the personal income tax and so no one would need to reinvent the wheel—nor be surprised at the easy likely outcome of such an audit," Shanske added, using the initials of the California Billionaire Tax Act.
Another drafter, UC Berkeley law professor Brian Galle, made a similar case to The New York Times Magazine, noting that Brin bought the Tahoe property only in December. "Spending time in your fifth vacation home does not a Nevada resident make," Galle said.
Critics, including Jared Walczak of the Tax Foundation, argue the January 1 residency date is vulnerable in court. In a recent paper responding to Walczak, Shanske, Galle and Gamage called that date "routine" in tax law. California's residency test, they wrote, turns on whether a person "intends to return" to the state, judged by the facts of their life.
With mail ballots being sent to voters, opponents are aggressively ramping up their campaign, spending or booking roughly $96 million of airtime and digital messaging, compared with just $209,000 by supporters, according to data compiled by the ad-tracker AdImpact.
A Tax on About 200 People
Proposition 40 would affect roughly 200 billionaires, with payments due in 2027 and an option to pay over five years. Real estate, pensions and retirement accounts are mostly excluded. About 90 percent of the revenue would go to health care. SEIU-United Healthcare Workers West (SEIU-UHW), one of the largest healthcare worker unions in the United States, sponsored the measure in response to federal Medicaid cuts. UC Berkeley economist Emmanuel Saez drafted it alongside Shanske, Galle and David Gamage of the University of Missouri.
“Are we destined to live in an oligarchic society begging for crumbs while our economic and political lives are controlled by a handful of the wealthiest people on Earth?” Sanders declared at one of three recent California rallies. “Brothers and sisters, that is the question on the ballot.”
Estimates of how much it would raise vary widely. Supporters project about $100 billion, while the Legislative Analyst's Office estimates "tens of billions of dollars." Stanford and Hoover Institution economists Joshua Rauh and Benjamin Jaros put the figure closer to $30 billion, arguing that wealthy residents leaving the state would reduce revenue over time.
Opponents have also backed two competing ballot measures, Propositions 41 and 42. If either receives more votes than Proposition 40, the billionaire tax would fail even if it wins a majority of votes.
"We’re not opposed to the concept of a wealth tax,” said Jodi Hicks, CEO of Planned Parenthood’s California chapter, to the Associated Press. “We just believe this proposal is seriously flawed and could do more damage than good.”
Brin is not the only wealthy donor funding the opposition. Venture capitalist John Doerr, former Google CEO Eric Schmidt and Stripe co-founder Patrick Collison have each contributed tens of millions of dollars. The Sacramento Bee reported that opponents were outspending supporters by at least 5 to 1. The Yes campaign, funded largely by SEIU-UHW, had raised about $32 million.
"Brin could have easily just run a No campaign and defeated [Prop 40], but he built a whole organization. They've awakened him. He wants to be a political player," Brandon Castillo, a veteran ballot-measure consultant who is not working on either side of the campaign, told Politico.
Recent polls show support for the tax slipping as Election Day approaches. In March, a Berkeley Institute of Governmental Studies poll found 52 percent of voters supported the measure and 33 percent opposed it. By September, support had fallen to 45 percent, while opposition had risen to 42 percent.
A Citrin Center/Politico poll released this week put support at 46 percent and opposition at 43 percent, within the margin of error. Nearly two-thirds of likely voters surveyed doubted the tax would remain a one-time levy, echoing a concern opponents' advertising has emphasized for months.
"With less than 50 percent support this close to the election, ballot measures for new taxes tend not to pass, as undecided voters likely break towards 'no,'" Berkeley IGS co-director Cristina Mora said in a September press release.
California voters rejected a similar tax proposal in 2022. Proposition 30, which would have raised taxes on incomes above $2 million, led in some late polling but ultimately lost by roughly 15 percentage points.
Democrats at War With Themselves
Brin's most important ally may be Newsom. The governor opposes Proposition 40, and on October 9 he endorsed Proposition 42, the countermeasure Brin largely funds.
The two men are old friends who attended each other's weddings, according to the New York Times, which reported that Brin took Newsom aside at a holiday party last year to complain about the tax. Weeks later, the governor came out against it. "This will be defeated," Newsom told the Times in January.
"I think billionaires do need to be taxed more, but just not at the state level," Newsom has said. His spokesperson told ABC News that the governor "supports a national tax on billionaires and is proud to stand with teachers, firefighters, reproductive health clinics, and others in opposing this poorly written state measure that will harm California."
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Teachers, firefighters and Planned Parenthood are with the governor, as is Xavier Becerra, the Democratic nominee to succeed him. The state Democratic Party, the California Labor Federation, Senator Bernie Sanders and Khanna are on the other side.
Khanna, a Silicon Valley congressman and possible 2028 presidential candidate, has turned the fight into a referendum on Newsom. "He doesn't want to offend some of the billionaires who he wants to finance his campaigns," Khanna told ABC News. "Are we going to be a party for the working class? Are we going to be beholden to our donors?"
Tiffany Jimenez, chief of staff at SEIU-UHW, also criticized Newsom directly. "They said Governor Newsom was going to keep the billionaire tax off the ballot. He didn't," she told Newsweek.
Sanders, campaigning in California this month, framed it more starkly: "Do you still have a democracy in this country, or will billionaires rule?"
Beyond California
No U.S. state has ever taxed billionaires on their net worth, and wealth tax bills from Senator Elizabeth Warren and Sanders are going nowhere in a Republican Congress. States have had better luck going after high incomes; Massachusetts' 2022 millionaire surtax now brings in more than $3 billion a year.
Saez, the Berkeley economist, has argued a win would push other states to follow and make billionaire taxes a central fight in the 2028 Democratic primary. Opponents say a loss would prove the idea can't survive even in a deep-blue state.
If Proposition 40 passes on November 3, legal challenges are all but certain, including over its residency rules. Under the measure, a billionaire disputing residency would generally have to pay the tax first and then sue for a refund, according to its drafters.
That could put Brin in the position of the Escondido couple in Bracamonte: proving to California's tax authorities that he had truly left before the clock ran out.
Newsweek’s reporters and editors used Martyn, our AI assistant, to produce this story. Learn more about Martyn here. Contact Newsweek editors on this story: Jason Lemon and Gray R. Thomas