Key keywords: Social Security solvency, stock market investment for public retirement funds, US Social Security reform, retirement benefit sustainability, equity market volatility risk, Social Security trust fund depletion, privatized Social Security proposals For decades, U.S. policymakers and economic analysts have debated potential solutions to the looming Social Security funding crisis, with the program’s Old-Age and Survivors Insurance (OASI) Trust Fund projected to be fully depleted by 2034 if no legislative changes are implemented. One of the most frequently floated proposals, particularly among fiscal conservative groups, is to allocate a portion of Social Security’s trust fund assets to public stock markets, or allow workers to divert part of their payroll tax contributions to private investment accounts, arguing that long-term average stock market returns of 7% annually (adjusted for inflation) would generate enough revenue to close the program’s $20 trillion long-term funding gap without raising taxes or cutting benefits. However, a new working paper published this month by the National Bureau of Economic Research (NBER) has thoroughly debunked this claim, after running over 10,000 simulations of market performance, policy design scenarios, and demographic shifts dating back to 1870. The research team found that stock market investment carries unacceptably high downside risk for a universal public program designed to provide a baseline of financial security for all retired and disabled Americans, and their surviving family members. First, the analysis revealed that periods of sustained market downturns, such as the Great Depression, the 2008 global financial crisis, and the 2022 bear market, could reduce trust fund assets by as much as 35% in a 10-year window if 40% of assets are allocated to equities, pushing the depletion date up by 2 to 5 years rather than extending it. Second, administrative costs for managing public or private investment accounts would eat into 0.4% to 1.2% of annual returns, erasing nearly a third of the projected gains from stock market exposure over a 50-year timeline. Third, private account proposals would disproportionately harm low-income workers, who have no other source of retirement savings to fall back on if their investments underperform, while high-income earners would see minimal impact to their overall retirement portfolios, widening existing wealth gaps in retirement security. The paper’s authors concluded that stock market investment, either at the trust fund level or via private accounts, is not a reliable solution to the Social Security funding crisis, and recommended evidence-based policy adjustments including raising the maximum taxable earnings limit for Social Security payroll taxes, implementing a modest 1 to 2 percentage point increase in the combined payroll tax rate, and adjusting benefit growth formulas for high-income earners to reduce long-term costs without harming vulnerable beneficiaries.