When Standard & Poor's downgraded America's credit rating, questions were raised about the agency's role in failing to blow the whistle on sub-prime mortgages. Now the Justice Department has launched an investigation of America's largest credit rating agency. At the same time, local governments are taking another look at whether S&P is serving their needs. Louise Story, who broke the news last night in the New York Times, has more on the investigation and on the ripple effect of the federal downgrade.