California voters have rejected Proposition 40, turning a proposed tax on billionaire wealth into a high-profile defeat for progressives—and a test of whether states can tax fortunes without driving them away.

The measure would have imposed a one-time 5% levy on California residents with at least $1 billion in net worth, excluding real estate and some retirement assets. Supporters projected up to $100 billion over five years, with most of the money directed to healthcare and the remainder to education, food assistance and administration. They argued that billionaires had benefited enormously from rising stock and business valuations while paying comparatively little tax on those gains. An open letter from economists said billionaires’ state income-tax payments from 2019 to 2025 amounted to “only 1.6% of their $1.4 trillion wealth gain.”¹

The liberal case therefore cast Prop. 40 as both a funding mechanism and a response to inequality. Its defeat, however, underscored the limits of that argument—even in a heavily Democratic state. The measure fractured its usual coalition: the California Democratic Party and some healthcare unions backed it, while Gov. Gavin Newsom, former Rep. Katie Porter, the California Medical Association and the California Teachers Association opposed it. Newsom preferred federal action and warned that a state-only tax could encourage wealthy residents and entrepreneurs to leave.

Opponents, including Google co-founder Sergey Brin and other technology billionaires, helped channel more than $250 million into the campaign against the measure. They argued that relocation would drain future income-tax revenue, jobs and investment. A Stanford study estimated that billionaires who had already left had removed roughly $540 billion from California’s potentially taxable wealth—and suggested Prop. 40 might raise closer to $30 billion than $100 billion.²

Conservative coverage framed the vote as rejection of a “pioneering wealth tax.”³ Another conservative headline called the proposal “TOO extreme even for California.”⁴ Yet the result does not settle the broader debate: it rejects California’s experiment while leaving federal taxation of extreme wealth firmly in Democratic politics.