Correction: An earlier version of this story incorrectly stated the amount the Congressional Budget Office had scored the Affordable Care Act in projected savings to Medicare over 10 years. This version has been corrected.

April 13, 2012

So why does a modest and short Post story about the health reform law become a blockbuster online? And what does that say about our reactive, partisan, hyperventilating media culture?

On Tuesday, below the fold on Page A3, The Post ran a story from its reporter on national financial and fiscal matters, Lori Montgomery, about a new study of the Patient Protection and Affordable Care Act, derisively called Obamacare but known among policy wonks as the ACA.

The study, by Charles Blahous of the free-market-oriented Mercatus Center at George Mason University, put meat and numbers on the bones of a Republican argument, made since 2009, that the act will add to the deficit. Blahous said that it will add at least $340 billion, and perhaps as much as $527 billion, to the deficit over 10 years.

This is contrary to what President Obama, and the nonpartisan analysts on Capitol Hill at the Congressional Budget Office (CBO), have said — that the act will cut the deficit over the first 10 years by a modest $132 billion. Indeed, that was one of the selling points of the law.

The crux of the argument is over how the CBO “scores,” or counts, the projected savings to Medicare, obtained by a set of arcane reforms that are projected to save about $575 billion over 10 years. There has been legitimate discussion, by the CBO and by Richard S. Foster, the chief Medicare actuary, about how to score the projected savings and whether the CBO “double-counts” them. Republicans say yes, it’s an accounting trick, Democrats and the CBO say no, it’s the only realistic way to do it. Neither party has asked the CBO to change the way it scores, by the way.

Putting the story on A3 was the right judgment for a print publication. Montgomery urged her editors, correctly, not to put it on the front page: it wasn’t worth that.

But that’s so old-media. On The Post’s Web site, the story took off, even though it was prominent on the home page for only a short time. It immediately entered the partisan spin cycle of exaggeration, distortion and hyperbole.

First, conservative blogger Matt Drudge linked to it with this subtle headline: “Obamacare explodes deficit.” A Forbes magazine blogger, The Post’s own Jennifer Rubin and conservative Web sites then jumped on it.

Liberals launched their counterattack. Jonathan Chait at New York magazine rebutted it; Paul Krugman of the New York Times linked to Chait, and then all manner of liberal Web sites piled on, including Media Matters.

If the right’s line of attack was, “See, we’re right, the president is lying about the costs of Obamacare,” then the left’s was more a guilt-by-association smear.

Charles Koch, one of the famously wealthy and libertarian-oriented Koch brothers, sits on the board of the Mercatus Center. And Blahous is a George W. Bush loyalist; he was deputy director of Bush’s National Economic Council and helped Bush push for the privatization of Social Security. Earlier in his career he worked for Alan Simpson of Wyoming and Judd Gregg of New Hampshire, two conservative Senate Republicans who often worked across the aisle with Democrats. And Blahous is the designated Republican member, named by Obama, of the Medicare Board of Trustees.

Most of my e-mails last week were from left-leaning readers snarking at The Post for running the story. The most amusing was this critic who accused Montgomery of being a “Koch teabagger shill; miserably lying IDJIT.” Yes, that was the spelling. You gotta laugh.

We in the media like the Web traffic that a story like this attracts. It quickens the media pulse; we all get a frisson of pleasure from being viral on the Internet for a day.

But I’m not sure the truth wins. The truth is that every complex law change, every annual federal budget, is a risk. They’re all based on assumptions and forecasts that may or may not come true. And when they don’t, Congress and the president have to adjust.

As the Medicare actuary wrote in his 2011 testimony: “The Affordable Care Act improves the financial outlook for Medicare substantially. However, the effects of some of the new law’s provisions on Medicare are not known at this time, with the result that the projections are much more uncertain than normal, especially in the longer-range future.”

Patrick B. Pexton can be reached at 202-334-7582 or at ombudsman@washpost.com. For updates, read the omblog at www.washingtonpost.com/blogs/omblog.