California's Proposition 40 could reshape state taxation forever, but will it actually survive the courts? The latest analysis from the National Taxpayers Union (NTU) on California’s proposed 5% wealth tax (Proposition 40) reveals massive structural and constitutional flaws. While the proposal aims to generate a $100 billion windfall by targeting the top 200 billionaires, the reality of implementation looks like an administrative and legal nightmare. Proposition 40 demands a 5% tax on total net worth, meaning privately held businesses, intellectual property, and highly volatile assets like crypto are fair game. The Franchise Tax Board has no existing infrastructure to accurately value these illiquid assets, setting the stage for years of costly litigation. Even good-faith valuation disagreements could trigger ruinous consequences. Understatements of tax face aggressive 20% to 40% penalties, and even the appraisers face separate financial penalties, which will make securing third-party valuations incredibly difficult and expensive The NTU has identified at least eight distinct grounds for legal challenge, including violations of the Due Process and Commerce Clauses. Most glaring is the retroactive residency snapshot (taxing 100% of worldwide wealth based on residency as of January 1, 2026, regardless of when the wealth was accumulated). Despite the advertised $100 billion gain, independent studies suggest that capital flight and the loss of standard income/sales tax revenue from departing residents will actually result in a net revenue loss of $25 billion for the state. Wealth taxes historically fail on the global stage as 12 OECD nations levied them in the 1990s; only 4 do today. But until the courts strike this down, proactive defense is mandatory.