Standard & Poor’s announced Friday night that it has downgraded the U.S. credit rating for the first time, dealing a symbolic blow to the world’s economic superpower in what was a sharply worded critique of the American political system.

Lowering the nation’s rating to one notch below AAA, the credit rating company said “political brinkmanship” in the debate over the debt had made the U.S. government’s ability to manage its finances “less stable, less effective and less predictable.” It said the bipartisan agreement reached this week to find at least $2.1 trillion in budget savings “fell short” of what was necessary to tame the nation’s debt over time and predicted that leaders would not be likely to achieve more savings in the future.