California's billionaires have mounted a formidable defense against a proposed wealth tax, pouring millions into a campaign to defeat the measure that would require them to pay 5% of their net worth. The initiative, Proposition 40, targets residents with assets over $1 billion and aims to raise funds for healthcare programs across the state. Recent campaign finance filings reveal that venture capitalist John Doerr, worth an estimated $22.6 billion, contributed $7.5 million to the political action committee Building a Better California. Chris Larsen, executive chair of blockchain firm Ripple and worth $11.4 billion, added another $10 million. Other wealthy individuals, including Lookout co-founder John Hering and Greenoaks Capital founder Neil Mehta, also chipped in with $946,000 and $250,000 respectively. The PAC, formed earlier this year to oppose Proposition 40, has built a war chest of $110 million as of late June, a clear indication that the state's richest residents view the tax as a significant threat to their fortunes. The tax would apply only once, but its impact on billionaires' holdings would be substantial, potentially forcing them to liquidate assets or relocate. A poll by UC Berkeley's Institute of Governmental Studies found voters evenly divided: 48% of likely voters support the measure, while 41% oppose it. The split falls heavily along party lines, with nearly all Democrats backing the tax, only half of unaffiliated voters in favor, and 80% of Republicans against it. Eric Schickler, co-director of the institute, noted that the outcome hinges on whether opponents can sway enough Democratic-leaning voters. To hedge their bets, Building a Better California has also backed two counter-initiatives: Proposition 41, which would require state auditor review of special tax proposals, and Proposition 42, which would ban taxes based solely on asset ownership. If either receives more votes than Proposition 40, it would nullify the billionaire tax even if the tax itself passes. However, voter awareness of these alternatives is low—only a third of voters have heard of them. The PAC has reserved $87 million in advertising time to sway public opinion before November. Political heavyweights are divided. Governor Gavin Newsom and Democratic candidate for governor Xavier Becerra oppose the tax, but the California Democratic Party recently endorsed it, a blow to billionaire opponents. Among the most vocal critics is Google co-founder Sergey Brin, who has moved assets out of California and contributed $102 million to the opposition effort. Former Shark Tank star Mark Cuban warned that the tax would drive entrepreneurs away, writing on X that "only idiot startup founders stay in Cali" if it passes. On the other side, Senator Bernie Sanders, along with Representative Ro Khanna, has introduced a national version of the tax, the "Make Billionaires Pay Their Fair Share Act," which would impose a 5% wealth tax on America's 938 billionaires to expand Medicare and provide direct payments to lower-income households. The battle over Proposition 40 has become a high-stakes test of whether California's progressive tax ambitions can overcome the financial firepower of its wealthiest residents.