Standard and Poor's is cutting the credit rating of the world's largest economy from triple A to double A plus.
The White House stayed silent in the immediate aftermath of the downgrade.
Republican presidential candidates campaigning in Iowa had plenty to say.
Republican presidential candidate Tim Pawlenty said, "This is a sad moment for the United States of America but it's a sad reflection of the trouble the country is in. It's a reflection of the failed leadership of President Obama. He really is inept when it comes to the economy."
Republican presidential candidate Rick Santorum said, "This is a real blow to the American economy, to our status in the world, and the president has to be held accountable for it. He did not provide leadership."
The unprecedented cut to the US AAA rating by a major ratings agency comes just 15 months before the next presidential election.
The downgrade and the nation's debt are certain to be the top issues for debate.