Decades of excessive spending by Congress has caused Moody's to lower America's credit rating. We'll look at federal revenue and spending over the past 59 years.

The dip in the U.S. credit rating indicates that ratings agencies believe the government is at a higher risk of default on its debt. While the U.S. rating still remains relatively high, the decrease may make investors more hesitant to lend to the government, and demand higher compensation for lending in the form of higher interest rates.