China, the largest foreign holder of United States debt, said Saturday that Washington needed to “cure its addiction to debts” and “live within its means,” just hours after the rating agency Standard & Poor’s downgraded America’s long-term debt. Though Beijing has few options other than to continue to buy United States Treasury bonds, Chinese officials are clearly concerned that the country’s substantial holdings of American debt, worth at least $1.1 trillion, are being devalued. “The U.S. government has to come to terms with the painful fact that the good old days when it could just borrow its way out of...