The U.S. and Japan carried out their first joint effort in a generation to boost the yen on Friday after the currency slid to a 40-year low, threatening to push up U.S. interest rates and disrupt Japanese investment flows into America. The yen had weakened to nearly 164 to the dollar, its weakest level since 1986, before the coordinated intervention.

Earlier solo attempts by Tokyo had failed, fueling anxiety over faster inflation and a swelling energy import bill as conflict with Iran squeezes oil supplies. By Monday afternoon in Asia, the yen had recovered to around 156 per dollar. Treasury Secretary Scott Bessent, who built his fortune trading currencies for George Soros's firm, declared the administration would not hesitate to intervene again to "correct the substantial undervaluation of the Japanese yen."

The move signals President Trump's willingness to aid allies battling financial markets, a departure from the hands-off stance long favored by U.S. policymakers except in moments of exceptional peril. Bessent emphasized on X that "The Trump administration delivers for America's trusted partners."