Could the largest foreign buyer of American debt suddenly stop buying? Here is a comforting thought: This problem is probably already behind us.

At a time when government issuance is massively expanding and firms face a 2025 refinancing cliff, overseas investors have gone from holding 43% of U.S. debt a decade ago to holding just 30%. Adding to the worries, the Bank of Japan might start raising interest rates next year, giving some Japanese owners a reason to repatriate their money.