CNBC's Morgan Brennan updates on Moody's downgrading U.S. credit rating.

Moody’s has downgraded the nation’s credit rating one notch to Aa1, leaving the U.S. without a top grade among any of the major rating agencies.

"Successive US administrations and Congress have failed to agree on measures to reverse the trend of large annual fiscal deficits and growing interest costs," Moody's said. Moody's was the last among major ratings agencies to keep a top,