Social Security reform usually involves politically difficult choices such as raising payroll taxes, reducing future benefits, or increasing the retirement age.
Senators Bill Cassidy of Louisiana and Tim Kaine of Virginia have promoted a less conventional idea. Their proposal would borrow about $1.5 trillion, invest it in a professionally managed fund, and allow the assets to grow for 75 years.
Supporters believe long-term market returns could help protect scheduled benefits without an immediate tax increase. Critics say the plan does not fix Social Security’s underlying imbalance and could leave future taxpayers responsible for trillions of dollars in added debt.
The proposal starts with borrowed money
Cassidy’s “Big Idea” would establish an investment fund separate from the existing Social Security trust funds.
The federal government would borrow approximately $1.5 trillion and invest it in a diversified portfolio. Cassidy has previously described funding it over 5 years, while a joint outline with Kaine referred to an upfront investment.
The fund would hold stocks, bonds, and potentially other assets. Investment gains would remain in the account rather than being used immediately to pay retirees.
Market gains would need to beat interest costs
The financial theory behind the proposal is straightforward.
Stocks have historically produced higher long-term returns than Treasury securities. If the fund earned more than the government paid in interest on its borrowing, the difference could eventually help Social Security.
However, the return advantage is not guaranteed. Weak markets, prolonged inflation, high interest rates, management expenses, or slower economic growth could reduce or eliminate the expected gains.
Taxpayers would still owe the Treasury debt even if the fund lost value or failed to grow as projected.
The plan uses a railroad comparison
Cassidy has compared the proposal with the National Railroad Retirement Investment Trust, which Congress created in 2001.
That trust invests railroad retirement assets in domestic and international stocks, bonds, private equity, and other investments. Its diversified structure allows it to earn more than a portfolio limited to federal securities.
The systems have important differences. Railroad retirement assets come from industry contributions and taxes rather than entirely from new federal borrowing.
The railroad system also has an automatic safety mechanism that can increase employer and worker tax rates when its reserves fall too low. The Cassidy and Kaine outline has not included a comparable automatic adjustment.
Total borrowing could be much larger
The initial $1.5 trillion would represent only one part of the government’s potential borrowing.
Social Security is projected to collect less in dedicated revenue than it owes in scheduled benefits. Under the investment concept, the Treasury could continue borrowing to cover those annual gaps while the new fund remained untouched for 75 years.
Researchers at Boston College estimated that maintaining full scheduled benefits could require another $25.1 trillion in borrowing over that period. Including the initial investment would raise modeled borrowing to approximately $26.6 trillion.
That estimate is based on long-term assumptions rather than an official congressional cost score. Actual borrowing could be higher or lower.
Simulations show a meaningful risk
Boston College researchers tested the proposal across thousands of possible market outcomes.
Assuming stocks earned an average inflation-adjusted return of 6.5%, the fund accumulated enough to cover all modeled borrowing in about 36% of simulations. With a more cautious 4% real return, it succeeded in roughly 17% of outcomes.
American Enterprise Institute researcher Andrew Biggs conducted a separate analysis and estimated full repayment in about 30% of the scenarios he examined. His modeling also found a little but serious possibility of extremely large remaining debt after 75 years.
The simulations do not predict exactly what markets will do. They demonstrate how strongly the proposal depends on returns exceeding borrowing costs over many decades.
Social Security faces an earlier deadline
The 2026 Social Security trustees projected that the Old-Age and Survivors Insurance Trust Fund would deplete its reserves in the fourth quarter of 2032.
Social Security would not disappear after that date. Ongoing payroll tax revenue would still be sufficient to cover about 78% of scheduled retirement and survivor benefits, leaving an immediate funding gap of approximately 22% if Congress took no action.
The proposed investment fund would not generate sufficient spendable gains to solve that 2032 problem on its own. Congress would still need to borrow, raise new revenue, make benefit changes, or adopt another temporary financing measure to maintain full payments while the fund grew.
The core imbalance would remain
The publicly described investment proposal does not include a specific payroll tax increase or scheduled benefit reduction.
That makes it politically appealing, but it also leaves the basic problem unresolved. Social Security is projected to pay more in benefits than it receives in dedicated income as the population ages and the number of workers supporting each beneficiary declines.
Investment returns could supplement a broader reform package. They cannot guarantee solvency without addressing what happens when returns disappoint or program costs continue exceeding revenue.
Cassidy and Kaine have promoted the concept as part of a bipartisan effort rather than a final stand-alone solution. Congress would still need to decide who manages the fund, what it can buy, how to prevent political interference, and who covers any shortfall.
TL;DR
- Cassidy and Kaine support a separate Social Security investment fund.
- The government would borrow about $1.5 trillion to create the fund.
- The assets would remain invested for approximately 75 years.
- Total modeled borrowing could reach about $26.6 trillion while maintaining full benefits.
- Independent simulations found that complete repayment occurred in a minority of tested outcomes.
- Social Security’s retirement trust fund is projected to deplete its reserves in late 2032.
- The investment proposal could supplement reform but would not eliminate the need to address taxes, benefits, or future borrowing.
