In testifying before the Senate Budget Committee Thursday, Treasury Secretary Timothy Geithner made a candid admission, characterizing President Barack Obama's own budget plan as "unsustainable" with interest payments and obligations that are "excessively high":

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A graphic from the committee's GOP majority illustrates the threat of growing debt as interest payments exceed total budget spending for 15 federal agencies:

Geithner also urged caution in the ongoing debt limit fight. "I would caution everybody against taking any risk that Congress does not act to increase the limit in the time frame we need," Geithner told the committee.

"We cannot afford to let the markets lose any confidence that ultimately the Congress will act well in advance of any time that we're going to hit the limit," he added, "because that would be catastrophic, and cause grave damage to the expansion underway."