It's the age of civility in American politics, but there's one institution that's been civil all along: the Congressional Budget Office (sorry, but sometimes civility is boring). The nonpartisan agency, which calculates the official cost of legislation for Congress, speaks in the polite language of actuarial tables, refuses to reliably please or disappoint either party and is the closest thing American politics has to an umpire. And the Republicans are getting sick and tired of it.

The reason is the health-care reform law. The CBO trashed the Democrats' first few attempts at a fiscally responsible bill, refusing to agree that various technological improvements Democrats were making to the medical system - like electronic health records - would save the money Democrats said they would. That sent the disappointed Democrats back to the drawing board - and more than once. But they eventually came up with a blunter,surer financing strategy: About $500 billion in cuts and reforms to Medicare, and a similar amount in new taxes. It was proof that the system had worked: Democrats, despite knowing that the taxes and Medicare cuts would cause them great political pain, were so intent on getting the Good Housekeeping seal of approval from the CBO that they made their bill far more fiscally responsible.

This left the Republicans in a bind. If the Democrats' legislation fulfilled its goal of covering almost every American and also managed to pay for itself, it was suddenly much harder to oppose. So last week, as the Republicans sought to make their case that the health-care bill should be repealed, a lot of their arguments were aimed at undercutting the numbers coming out of the CBO.

The agency's product is nothing more than "budget gimmicks, deceptive accounting, and implausible assumptions used to create the false impression of fiscal discipline," conservative wonks Douglas Holtz-Eakin, Joseph Antos and James C. Capretta wrote in the Wall Street Journal. Rep. Paul Ryan (R-Wis.) says the CBO's numbers are based on "smoke and mirrors." Rep. Louie Gohmert (R-Tex.), angry that the CBO thinks tax cuts reduce tax revenue - no doubt the agency has also been known to say that the sun rises in the east - has called for the CBO to be abolished.

The sad reality is that it's not hard to discredit budget estimates in 30-second sound bites: You just say whatever you want and trust that your opponent doesn't have anywhere near enough time to explain the issue. Take Republican criticisms that the "doc fix" isn't included in the CBO's scores, and that if it were, the health-care bill would increase the deficit. It's absurd. In 1997, congressional Republicans capped the rate at which Medicare could increase payments to physicians. But their cap was too low. Now they want Democrats to fix it for them and pile the costs onto the bill. It's a little like saying that the cost of the war in Iraq should be added to health-care reform.

But you'll notice it took a moment to explain that. It's easier to just say that the score is full of "smoke and mirrors" and then make some authoritative-sounding point about Medicare payments. Who's got the time to check it out?

You can play whack-a-mole with this stuff all day. But beneath it is something more insidious: an effort to discredit the last truly neutral, truly respected scorekeeper in Washington. The facts don't support the particular case the Republicans want to make, so they're trying to take down the people who supply the facts. But once that's done, it can't easily be undone. And the true loser will be the very thing Republicans claim to care most about: the deficit.

If getting the CBO's seal of approval ceases to matter, then political parties will cease to try. That's when the "smoke and mirrors" will really begin: when bills just have to sound good rather than pencil out. When there are no skeptical budget experts sending legislation back to the authors with a note that says "Sorry, not there yet." When policy debates are decided by who can yell the loudest rather than who can write the best bill.

The bargain that both parties have struck with the CBO is that they'll accept the short-term setbacks the agency imposes on them because, in the long run, it's better for the system to have someone keeping score. Right now, Republicans are breaking that bargain. They're not merely saying that the CBO's guess is bad, or that the CBO is right but the bill is bad for other reasons, but that the CBO's whole system is, in the words of Rep. Tom Price (R-Ga.), "Garbage in, garbage out." Civil? Maybe. Wise? Definitely not.