Social Security’s primary trust fund will be depleted in 2032, according to the 2026 Trustees Report. At that point, benefits will be cut across the board by 22 percent, as the program will only be able to disburse what it collects in annual revenues. Given Social Security’s unsustainable finances, some policymakers have proposed incorporating stock market investments as part of a solution.

In 2025, Senator Bill Cassidy (R-LA) and Senator Tim Kaine (D-VA) penned an op-ed in the Washington Post detailing a bipartisan plan aimed at fixing the projected shortfall for the country’s largest program. The plan proposes borrowing $1.5 trillion upfront, investing that sum, and leaving both the principal and gains untouched for 75 years to allow long-term returns to accumulate. To meet annual obligations to Social Security recipients, (and leave benefit amounts unchanged) the trust funds would borrow the amount that incoming revenues do not cover. Such borrowing is estimated to total $25.1 trillion over 75 years, resulting in $26.6 trillion in total borrowing in the Cassidy-Kaine plan.

In response, The Center for Retirement Research at Boston College (CRR) published a report concluding that the Cassidy-Kaine plan is unlikely to fix Social Security’s financing problems. In fact, their analysis shows that the proposal would likely leave the country with more debt than before.

CRR modeled potential outcomes for three different underlying scenarios. For each of the scenarios, the model ran 10,000 simulations and assessed the probability, or odds, of paying back the borrowing. In the stated Cassidy-Kaine proposal, the plan assumes the stock market will have future returns that equal historical returns. It also assumes an interest rate that is unaffected by the plan’s extensive borrowing. According to CRR, the odds of repaying the full amount borrowed in that scenario are only 36 percent.

CRR then modeled the likelihood of paying back the borrowing in two other scenarios. In the second, the future real return rate is not the historical rate of 6.5 percent, but instead a rate determined by academics and practitioners derived from the relationship between market value, stock returns, and gross domestic product (GDP). Using that methodology, CRR determined a 4 percent return rate. With a lower return rate but the same interest rate, the odds of paying back the borrowing drop to 17 percent.

The third scenario incorporates the effect of borrowing into the underlying assumptions. With such considerations, the real return rate drops to 3.5 percent because of lower GDP growth and higher interest rates, which rise from 2.3 to 2.6 percent. In that scenario, the Cassidy-Kaine plan does not repay the full $26.6 trillion in any outcome.