The Japanese yen fell to a 40-year low near 164 per dollar before the United States joined Japan in buying the currency on July 31, and Treasury Secretary Scott Bessent now says the operation was intended to prevent that slide from raising borrowing costs for Americans. In an August 27 response to congressional questions that became public Friday, Bessent argued that disorderly currency moves could force investors to unwind leveraged positions and destabilize global markets, according to Reuters. The intervention briefly lifted the yen to 155.20, but it has since weakened back toward 160.

The letter supplied the administration's clearest public rationale for a highly unusual use of the Exchange Stabilization Fund, or ESF. Bessent said Treasury exchanged foreign-currency assets already held by the fund for yen; it did not make Japan a loan that Japan must repay. That distinction directly answers one premise in Senator Elizabeth Warren's August 13 letter, which asked about taxpayer exposure, the legal basis for the transaction and the amount committed. Treasury still has not publicly disclosed the size or current value of the U.S. position.

The dispute is larger than a technical argument about foreign exchange. Japan is the largest foreign holder of U.S. Treasury securities, so a rush by Japanese institutions or authorities to sell dollar assets could push American yields higher even if the initial disturbance begins abroad. Bessent's defense therefore rests on prevention: accepting a limited market risk through the ESF to reduce the chance of a more expensive disruption in Treasury markets. The evidence shows that intervention changed prices quickly, but not that it permanently corrected the forces weakening the yen.

How Treasury Bought Yen

Foreign-exchange intervention is a direct market transaction, not an interest-rate decision. Japan's Finance Ministry said in an official statement that it bought yen in coordination with Treasury to counter excessive volatility and disorderly movements. To support the yen, the U.S. side sold other foreign-currency assets and purchased yen, reducing the relative supply of dollars or euros offered against Japan's currency and signaling that two major governments were prepared to resist a one-way trade. The market impact depends as much on credibility and surprise as on the cash deployed.

The operational chain gives Treasury broad control. The Federal Reserve Bank of New York executes trades as the government's fiscal agent when directed by Treasury, while the ESF owns the assets and bears the resulting gains or losses. The fund's statutory authority permits the Treasury secretary, with presidential approval, to deal in foreign exchange and other instruments when consistent with U.S. obligations to promote orderly exchange arrangements. Unlike an ordinary appropriated program, the ESF can act quickly from an existing pool of reserves without Congress passing a new spending bill for each transaction.

Why a Weak Yen Can Reach U.S. Borrowers

The administration's transmission argument begins with Japan's enormous financial system. Japanese banks, insurers, pensions and public institutions hold large volumes of overseas assets, including U.S. government bonds. A rapid yen decline can raise hedging costs, trigger margin demands and make investors close positions financed with cheap yen. If enough holders sell Treasuries at once, bond prices fall and yields rise; those yields feed into mortgages, corporate debt and other American borrowing costs. This pathway is plausible, but the letter does not quantify how close markets were to such a forced unwind.

Japan's commitment has been far larger and more visible than Washington's. Finance Ministry data showed that Tokyo spent 15.4 trillion yen, or about $96.5 billion, intervening between July 30 and August 26, a monthly record. The currency moved from roughly 163 per dollar to 155.20 after the coordinated action, then settled near 159.50 before slipping further. That pattern shows a meaningful short-term effect, but it also demonstrates the limit of purchases that are not reinforced by a durable change in monetary, fiscal or trade fundamentals.

A Rare Tool With Broad Authority

Direct U.S. intervention in major currencies has become exceptional. The last coordinated U.S.-Japan operation to strengthen the yen occurred in 1998, when Treasury records show American authorities bought $833 million of yen after the currency approached 146 per dollar. The United States joined a broader Group of Seven action in 2011, but that intervention moved in the opposite direction, weakening the yen after Japan's earthquake and tsunami. July's purchase therefore revived a tool that had not been used to support Japan's currency for nearly three decades.

The Fed guidance makes clear that this repo backstop is separate from the ESF's currency purchase. FIMA transactions are conducted only in dollars, fully collateralized by Treasuries and publicly reported in aggregate, leaving the Federal Reserve without foreign-exchange risk. An ESF purchase of yen, by contrast, changes Treasury's currency exposure and can produce a valuation gain or loss. Combining the two tools may reduce pressure on Japan to sell Treasuries, but it does not make the yen intervention itself risk-free.

The Oversight Questions Still Open

Warren asked Treasury to disclose the amount purchased, the legal analysis supporting the action, the expected taxpayer cost and whether the European Central Bank was consulted before euros were sold. Bessent's response addressed the alleged loan risk and offered a systemic-risk explanation, but the public reporting does not show that he supplied a transaction amount. Without that figure, Congress cannot compare the potential market benefit with the fund's actual exposure or assess how much capacity remains for another round.

The effectiveness test is also unsettled. Intervention clearly produced an immediate appreciation and forced some investors betting against the yen to retreat. Yet the subsequent slide toward 160 indicates that market participants still see the U.S.-Japan interest-rate gap and Japan's domestic policies as dominant. A temporary reversal can still be useful if it prevents disorder and gives policymakers time, but a lasting exchange-rate target would require repeated purchases or changes in the economic conditions that created the imbalance.

Nor does the exchange-rate move alone prove that American borrowing costs were protected. Establishing that claim would require evidence that Treasury sales were imminent, that yields would have risen materially without intervention, or that market liquidity improved because of the joint action. Bessent described the mechanism and the risk he sought to avoid; he did not present a counterfactual that can be observed directly. That limitation is inherent in preventive financial policy, but it increases the importance of disclosing inputs, limits and results after immediate market danger passes.

What Will Determine Whether the Policy Worked

The next test is whether Japan's central bank narrows the interest-rate gap that has sustained the yen trade. Markets have assigned substantial odds to a September rate increase, and Japanese officials have said currency policy will be aligned with monetary policy. A rate rise would make yen-funded positions less attractive and could validate the intervention as a bridge to a more durable adjustment. Another delay, especially alongside higher U.S. rates, would leave authorities confronting the same pressure with more reserves already committed.

Disclosure will be the second test. Treasury and the Federal Reserve publish quarterly reports on foreign-exchange operations, while Japan plans a detailed daily breakdown of its recent interventions later this year. Those records should reveal the U.S. amount, the assets sold, the valuation of the yen position and whether further trades occurred. They will also allow Congress to separate the ESF's market exposure from FIMA lending that is collateralized by Treasuries.

Bessent has now articulated a coherent public-interest case: a disorderly yen decline could spill into U.S. bond markets, and a reserve exchange may be cheaper than managing the resulting instability. The July action also remains an incomplete policy experiment. Its immediate price effect was real, its lasting currency effect has faded, and the federal government has not disclosed enough information to measure its risk or contribution. The intervention's ultimate credibility will depend less on the force of Treasury's defense than on transparent accounting and economic policies capable of sustaining the market signal.