Throughout the course of the Bush years, the Republican Party, which now puts its stock in the CBO's numbers, continuously marginalized the organization for its accounting.

When the CBO predicted in 2004 that Bush's new tax and spending proposals would produce deficits of $2.75 trillion over ten years, a spokesman for the White House Office of Management and Budget declared that ''even CBO would admit we don't honestly know what these numbers will look like 10 years from now.''

That same year, the Bush administration pushed forward with its plans for Medicare Part D despite the fact that its internal cost estimates were $139 billion more than those offered by the CBO. Republicans on the House Ways and Means Committee had worked diligently to defeat the attempts of their Democratic colleagues to make those estimates public.

In a similar vein, conservatives were beside themselves when the CBO refused to run the 2004 Bush tax cuts through various economic models to see if the government could, in the end, make money by stimulating spending. Rather, the CBO used a "static" method and found $1.2 trillion worth of deficits through the next decade. Republicans, naturally, largely ignored the findings.

Perhaps the biggest caution flag for treating CBO numbers as gospel -- and one of the more illuminating benchmarks from which to compare the current debate over health care costs -- is the Iraq War.

In October 2003, the CBO was asked to do a study about the costs of the Iraq War. According to varying scenarios of troop deployment the total price tag ranged from $85 billion to $200 billion over a ten-year period. A year later, the projected costs had risen further. Having already spent $123 billion, the CBO was now estimating that the prosecution of both Iraq and Afghanistan would total roughly $1.1 trillion over the subsequent ten years.

"In the scheme of things, the war is not super-expensive, but it also sure ain't cheap," said Michael O'Hanlon, a Brookings Institution scholar and prominent war supporter.