Treasury yields are already blowing up the CBO’s long-term forecasts, and experts who previously downplayed U.S. debt fears are now starting to worry

Add it all up, and the future looks more expensive. The Committee for a Responsible Federal Budget estimated that if yields remain more than 80 basis points over baseline projections, the U.S. will spend $2.7 trillion on annual interest payments by the end of the decade—more than Medicare or Social Security retirement benefits. “The real threat is the debt spiral. If interest begets debt, and debt begets interest, eventually debt will spin out of control. A fiscal crisis, once unthinkable, is now a distinct possibility,” Maya MacGuineas, president of the CFRB, said on Monday. The budget watchdog and others have...