Standard & Poor's decision on Friday to downgrade the U.S.'s formerly top-notch credit rating has ignited a war of words as politicians and some prominent investors have questioned the credit-rating agency's trustworthiness. "The people who rated subprime-backed securities are now declaring that they are the judges of fiscal policy? Really?" wrote Paul Krugman in The New York Times. Other analysts defended the agency, saying the move was warranted.