In a speech unveiling his debt-reduction plan earlier this week, President Obama fleshed out what he described as a simple principle on tax fairness: “Middle-class families shouldn’t pay higher taxes than millionaires and billionaires. That’s pretty straightforward. It’s hard to argue against that. Warren Buffett’s secretary shouldn’t pay a higher tax rate than Warren Buffett. There is no justification for it. It is wrong that in the United States of America, a teacher or a nurse or a construction worker who earns $50,000 should pay higher tax rates than somebody pulling in $50 million.”

The Associated Press ran a fact-check piece yesterday, making the case that the president’s claim was wrong — Obama, the AP said, “makes it sound as if there are millionaires all over America paying taxes at a lower rate than their secretaries.” Since, on average, millionaires and billionaires shoulder a larger tax bill, the AP disapproved of the president’s rhetoric.

But the fact-check piece made a variety of unfair inferences. Obama never said every millionaire pays lower tax rates than every administrative staffer; he said it happens, it shouldn’t happen, and if we approve meaningful tax reform, it won’t happen.

Paul Krugman called the AP’s analysis “stupid.”

[W]e’re not talking about one or two exceptional guys, either. Look at the IRS data on returns for the 400 highest incomes in America (pdf) — specifically, Table 4. If you look at the numbers since 2004, you’ll see that in a typical year between 30 and 40 percent of those super-high-income players paid an average tax rate of less than 15 percent; most of them paid less than 20 percent. Bear in mind that for the very wealthy the payroll tax — the main burden on working-class Americans — is trivial, because of the cap on Social Security and the fact that it only applies to earned income. And what becomes clear is that the Obama/Buffet claim is absolutely, totally true.

So why the attack? Probably because it’s such an effective line. And we can’t have populism that actually strikes a chord with the public, can we?

It’s really not that complicated. Obama has endorsed something he calls the “Buffett Rule,” based on the notion that millionaires and billionaires “should not pay a smaller share of their income in taxes than middle-class families pay.” Arguing that this only happens some of the time isn’t much of an argument, from Republicans or from major media outlets.

It’s also worth noting that Media Matters made an interesting catch: after publishing the fact-check piece, “the AP has subjected it to heavy revisions. However, posts reporting the story at National Review Online, the Weekly Standard, and Hot Air all quote from the original version of the story, ensuring it will live on in conservative mythology.”

I’m generally quite fond of media outlets engaging in these fact-checking endeavors; it sure beats the mind-numbing “he said, she said” coverage that dominates political coverage. But if your fact checks need “heavy revisions,” you’re doing it wrong.

Steve Benen

Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.