Voters usually decide one or two income or wealth tax measures a year. This midterm season, there are nine

California’s billionaire tax has gotten the headlines, and the billionaires paying to stop it make up a good share of them. They’ve poured tens of millions of dollars into defeating Prop 40, a one-time 5% levy on their net worth to help offset federal cuts to health spending.

Google cofounder Sergey Brin and others are pushing efforts for Props 41 and 42, which would effectively stop Prop 40 were it to pass. But Prop 40 is one entry on a much longer list.

Voters in six states will decide nine statewide measures on income or wealth taxes this year. From 2000 to 2025, voters decided 40 such measures—a pace of roughly one and a half a year—and they’ve been evenly split: 20 approved, 20 defeated.

Lawmakers in these states haven’t been asking voters to raise taxes on the rich: most measures that would create or raise taxes were put there by citizen initiatives, created by activists and unions.

Growing political willpower

This year, there are measures to increase taxes on the rich in California, Colorado, Washington, Massachusetts and Cook County, Illinois.

California Gov. Gavin Newsom and Democratic gubernatorial candidate Xavier Becerra both oppose Prop 40, while the California Democratic Party endorsed it (Newsom has since backed........

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