The U.S. is caught in a spiraling debt crisis, and a major casualty might be demand for U.S. Treasuries—a critical support pillar for the economy and the government’s ability to spend money. The scale of U.S. borrowing is severely testing confidence in the country’s ability to keep financing itself. The federal debt has climbed to $39 trillion, a level that budget experts have warned might soon force the U.S. into increasingly dire decisions as to what it can spend on. One victim of such a spiral would ...