File under “D” for Duh.

This seems self-explanatory:

“The federal budget deficit is on an unsustainable path, in which large deficits result in rising interest rates and ever-growing interest payments that augment deficits in future years,” Greenspan said in his prepared testimony. “But most important, deficits as a percentage of [gross domestic product] in these simulations rise without limit. Unless that trend is reversed, at some point these deficits would cause the economy to stagnate or worse.”

Too bad Congress and President Bush don’t get it.