The US is selling euros to buy yen to avoid Japan having to sell off US treasuries to support their currency. As soon as the US can no longer support the yen, the US will potentially experience a rapid increase in US treasury rates if Japan starts selling off treasuries for liquidity to provide currency support, pushing up consumer borrowing costs and interest payments on the debt.
https://www.theguardian.com/world/2026/aug/03/trump-japan-cu...
https://www.pgpf.org/programs-and-projects/fiscal-policy/mon...