On August 5, 2011, representatives from S&P announced the company's decision to give its first-ever downgrade to U.S. sovereign debt, lowering the rating one notch to "AA+", with a negative outlook. The government was furious. Two weeks after the August, 2011 S&P downgrade, SEC and Department of Justice announced that S&P was under investigation, and the CEO of S&P was forced to resign just 18 days later.
Three years later, filed a $5 Billion lawsuit against the company.
You can bet that no ratings agency will ever do that again.