Back during the Great Recession of 2007-09, it became common for economists to talk about “financial plumbing” as part of the problem. The metaphor of pipes and drains and valves was meant to suggest that a relatively small blockage or capacity limitation in one part of the financial plumbing could lead to much bigger systemic effects. In other words, the financial plumbing might work just fine in ordinary day-to-day use, but if one part of the financial system came under stress, problems could back up unexpectedly.
With that general concept in mind, consider the total amount of US Treasury debt held by the public. Back in 2001, it was about $3.5 trillion. By 2009, it had doubled again to $7 trillion. By 2016, it had doubled again to $14 trillion. By 2024, it had doubled one more time to $28 trillion. The Congressional Budget Office forecasts suggest that by 2035, based on current law (that is, before the passage of this year’s budget and tax bills, which in their current form would increase the debt further), total US debt could nearly double one more time to $52 trillion.

So here’s the question: How confident should we be that the financial plumbing which handled the trading of US Treasury debt when the market was one-eighth of its current size, back in 2001, is equally capable of handling the much larger volume–especially when the market comes under stress? Darrell Duffie rings some warning bells in “How US Treasuries Can Remain the World’s Safe Haven” (Journal of Economic Perspectives, Spring 2025). (Full disclosure: I am the Managing Editor of JEP, and thus predisposed to find the articles of interest.)
If it seems far-fetched that the US Treasury market should come under stress, then it’s worth noting that it happened in March 2020. Duffie explains:
When the World Health Organization declared COVID-19 a global pandemic on March 12, 2020, … the dealers who make markets for Treasuries were unable to handle the flood of demands by investors around the world to buy their Treasury securities. Bond dealers were asked at the same time to buy enormous quantities of mortgage-
backed securities and corporate bonds, among other demands for liquidity. Total customer-to-dealer bond-market trade volumes suddenly jumped to over ten times their respective 2017–2022 sample medians (Duffie et al. 2023). The bond market reached the limits of its intermediation capacity and became effectively dysfunctional. Yields for Treasury securities lurched higher, while dealer-to-customer bid-offer spreads and dealer-to-dealer market depth worsened by factors of over ten (Duffie 2020). Among other steps to support the market, the Federal Reserve purchased almost $1 trillion dollars of Treasury securities from primary dealers in the first three weeks after March 12, freeing dealer balance-sheet space to handle more sales from customers. Weak market functionality persisted for several additional weeks (Duffie et al. 2023). Although liquidity in Treasury markets gradually returned to normal, many Treasuries investors presumably noticed that in the heart of the March 2020 crisis, they had not benefited from the safe-haven requirement of a liquid and deep market. Even before the COVID-19 crisis, the vaunted liquidity of the market for trading Treasuries had been showing cracks under stress.
Potential difficulties in the market for US Treasury bonds have large implications. As Duffie notes, many financial institutions and investors around the world view US Treasuries as their “safe” asset. Pretty much by definition, a safe asset holds its value and can be sold when desired. The ability of the US government to market its debt at favorable interest rates depends on this widespread perception. But if the market for Treasury debt can become illiquid in a crisis, as happened in March 2020, then Treasury debt is less safe than it previously appeared. The higher risk means that the US government would need to pay higher interest rates when it borrows.
As Duffie explains the plumbing in the market for Treasury debt, about $1 trillion is traded every day, and most of that flows through 25 firms that are designated as “primary dealers.” Essentially, this means that when there is a surge of sellers of Treasury debt, these primary dealers need to be financially able to act as immediate buyers–although of course they will be planning to re-sell most of that Treasury debt later. But the total amount of Treasury debt is rising fast, much faster than the financial size of the primary dealers. In 2007, before the Great Recession, the ratio of total Treasury debt to the assets of the primary dealers was less than 0.2; by 2023, the ratio was above 0.7. In short, the financial plumbing for the US Treasury market is running much closer to its capacity, and it has already gotten clogged once.
Of course, one way to make it easier for the primary dealers to guarantee that they will buy Treasury debt when needed would be to have less government borrowing and less Treasury debt. Now that we’ve all had a good giggle over the implausibility of that happening, what are the serious options? Ultimately, the goal might be to move beyond having the Treasury debt market flow through these 25 firms, and instead create an “all-to-all” market, more like the stock market, where buyers and sellers of Treasury debt can interact directly. But setting up such a market is nontrivial, and it still would raise the question of what happens in world financial markets if a wave of sellers of Treasury debt start driving down the price.
Duffie reviews a number of policy options, some of which are being implemented. You can read his article for details, but to give a sense of the possibilities:
- Require that trades for Treasury debt be carried out through a central clearinghouse, rather than as trades between two separate parties: “The clearinghouse offers a guarantee: if one of the original counterparties fails to perform at settlement, then the clearinghouse will complete the settlement.”
- “Regulators are slowly moving toward a plan for improving post-trade price transparency in the market for US Treasury securities by publishing trade price and quantities shortly after each trade (Liang 2022). Post-trade price transparency will likely improve competition and allocative efficiency. … The efficiency with which dealers are matched to trades will improve, likely expanding the intermediation capacity of the market. Eventually, greater post-trade price transparency will also speed up the emergence of all- to-all trade.”
- The Federal Reserve could set up arrangements to guarantee in advance that if/when US Treasury debt markets are melting down, they will extend short-term credit to key market players as needed. Experience has taught that when such backstop arrangements are known to be available in advance, they are less likely to become necessary!
- The US Treasury could buy back US Treasury debt issued in the distant past, which is harder to trade in the market, and replace it with newly-issued debt which is easier to trade in the market.
- Re-consider the specific bank supervision rules that try to make sure banks have sufficient capital to face crises, and make sure that these rules are not having the effect of discouraging banks from holding Treasury debt in a financial crisis situation.
Duffie says it bluntly: “The market for Treasury securities is simply growing too large to rely exclusively on dealers to intermediate investor trades.” Ultimately, the choice is whether financial regulators will proceed with all deliberate speed to implement the necessary changes before the next crisis hits the Treasury debt market, or whether the regulators will be improvising less-considered schemes when the next crisis hits the Treasury debt market.
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