**Proposition 40, the one-time 5% wealth tax on California residents with net worth above $1 billion as of January 1, 2026, faces significant structural and political hurdles ahead of the November 3 ballot.** Opponents have raised over $200 million, led by figures such as Sergey Brin, to fund two competing measures—Propositions 41 and 42—that could nullify the tax even if it secures a majority, depending on relative vote totals. Governor Gavin Newsom and several business and medical groups have opposed the initiative, citing risks of reduced income-tax revenue, asset valuation disputes, and potential litigation over the novel wealth assessment process. Recent polls show narrow support for Prop 40 alongside comparable backing for the countermeasures, leaving the outcome closely contested amid high spending and voter confusion over the linked proposals. Traders assign a 68.5% implied probability against passage, consistent with these implementation and electoral complexities.