On a jittery day for the financial world, it fell to Obama to deal with a downgrade that S&P had warned for weeks would come if Obama and Congress failed to agree on a major debt-reduction package. The agency was dissatisfied with the deal lawmakers reached last week to cut more than $2 trillion from the debt over 10 years.

The administration has derided the downgrade as having no economic basis. S&P, though, has little faith in Washington's ability to overcome its partisan woes on the debt.

"We didn't need a rating agency to tell us that the gridlock in Washington over the last several months has not been constructive," Obama said.

S&P has dropped the government's rating to AA+ from the top rating, AAA. The agency attached a negative outlook that means the rating could be lowered again.

Asked under what scenario the United States could regain its AAA rating, David Beers, head of sovereign ratings at S&P, told reporters on Monday, "We don't anticipate a scenario at the moment where the United States could quickly return to AAA."

S&P officials said that five countries including Canada and Australia have lost their AAA ratings from S&P and then regained them. The shortest time that it took a country to regain an AAA rating was nine years and the longest time was 18 years.

Wall Street had its first chance to react to the downgrade on Monday. The Dow fell below 11,000 for the first time since November. The sharp drop extended Wall Street's almost uninterrupted decline since late July, when the Dow was flirting with 13,000.

Republican candidates hoping to challenge Obama next year have placed blame for the downgrade on Obama, tying it to his larger economic agenda.

Former Massachusetts Gov Mitt Romney, who leads the Republican field in fundraising and early polls, said the downgrade was a "deeply troubling indicator of our country's decline under President Obama." Republican Rep Michelle Bachmann, who has shown strength in the early voting state of Iowa, accused Obama of "destroying" the US credit rating.

Obama calmly sought to dismiss all the talk of a dent to US credit.

"Our problems are eminently solvable," he said. "We know what we have to do to solve them. Our problem is not confidence in our credit. The markets continue to reaffirm our credit as among the world's safest. Our challenge is the need to tackle our deficits over the long term."