Treasury Secretary Timothy Geithner ripped Standard & Poor's two days after the ratings agency downgraded US debt, saying the stunning move was based on a "lack of knowledge" about the nation's finances.
Geithner also said the debt crisis presents Congress with a chance to "earn back confidence of investors around the world" and he reiterated his support for President Obama, who asked Geithner to stay on even as calls intensified over the weekend for his resignation.
"S&P has shown really terrible judgment and they've handled themselves very poorly," he said in an exclusive interview with CNBC. "And they've shown a stunning lack of knowledge about basic U.S. fiscal budget math. And I think they drew exactly the wrong conclusion from this budget agreement."
As he spoke, US stock futures indicated a sharply lower open for Wall Street as investors reacted to the move by S&P to strip the US of its coveted AAA credit rating.
However, Geithner said investors should continue to have full faith in US debt.
"The judgment by S&P changed nothing. It added nothing to what people know about this country," Geithner said. "Again, there's no risk the U.S. would never meet its obligations. We've got some challenges ahead of us, but we'll be able to work with those challenges. We'll get through this."
Yet even as he criticized S&P he acknowledged that public finances are in poor condition.
"There's no surprise that the U.S. has a long-term and unsustainable fiscal position," he said. "We believe that. The president believes that. That's why he's been fighting so hard to bring people together to try to deal with it.
He spoke amid fierce rancor in Washington.
Sen. John Kerry (D-Mass.) called the situation a "tea party downgrade," while Rep. Michelle Bachman, the tea party favorite from Minnesota and Republican presidential candidate, called on Obama to fire Geithner.
"I'm not going to do politics," Geithner said. "I think if we've learned anything these last few months it's it's time to put the economy ahead of politics. Again, these are challenges facing the country of the United States, not facing one party or the other. We both have some responsibility for coming together to dig our way out of this stuff."