In a surprise appearance before reporters at the White House just now, Obama made a striking, if perhaps long overdue, charge: He pushed back on GOP claims he’s running a dirty campaign by arguing that Romney’s entire campaign is based on flat out lies.

Obama was questioned sharply by a reporter who pointed to the Priorities USA ad featuring the dead woman and the Obama campaign’s pressure on Romney to release his tax returns, and asked whether he regretted his campaign’s tone. Obama responded, in part:

“I don’t think that Governor Romney is somehow responsible for the death of the woman that was portrayed in that ad. But keep in mind, this is an ad that I didn’t approve; I did not produce; and as far as I can tell, has barely run. I think it ran once. Now, in contrast, you’ve got Governor Romney creating as a centerpiece of his campaign this notion that we’re taking work requirement out of welfare. Which every single person here who’s looked at it says, it’s patently false...

“Everybody who’s looked at this says what Governor Romney is saying is absolutely wrong. Not only are his Super PACs running millions of dollars worth of ads making this claim; Governor Romney himself is approving this and saying it on the stump. So the contrast I think is pretty stark. They can run the campaign that theyw ant; but the truth of the matter is, you can’t just make stuff up. That’s one thing you learn as president of the United States. You get called into account.”

I’m pretty sure this is the first time Obama himself has charged that virtually Romney’s entire campaign is based on a “centerpiece” that’s flat out false.

It’s true that there's serious truth-stretching on both sides. I’ve said that the Priorities USA ad suggesting Bain is to blame for the steelworker’s wife goes too far. I agreed that the Obama ad labeling him as an “outsourcer in chief” was false. (The Obama camp has since tweaked his ads to make the language more defensible, arguing that Romney’s “companies” were called “pioneers in outsourcing.”) I thought it was unfair and misleading to quote Romney out of context this way: “I like being able to fire people.” I dismissed the present relevance of the story about Romney’s prep school bullying, which Dems pushed hard for days.

But it remains the case that we are seeing nothing from the Obama side that’s anything like what Romney is attempting. Romney right now is premising one of the central arguments of his whole campaign on a complete lie. The notion that Obama “gutted” the work requirement in welfare reform has been debunked again and again by independent fact checkers and by the president who signed the law Obama supposedly gutted (see Clinton, Bill).

But Romney has now run three ads — one, two, three — making this claim. Incredibly, the Romney campaign is doing this, even though he himself said that campaigns should pull ads that are called out by fact checkers. Romney and his surrogates have repeated the welfare lie in forum after forum after forum.

Steve Benen notes today that Romney is betting that “political journalism isn’t equipped to deal with a campaign predicated entirely on falsehoods,” and that his historic levels of mendacity poses a test for our political system. I’m inclined to agree.

The folks working at the big news organizations know Romney is lying with abandon. What should they do about it? I’m sympathetic to political journalists — it’s not easy to keep up with all the falsehoods, and at a certain point, the same lie told again and again loses its news value. But perhaps Obama’s comments today will prompt at least a bit of media discussion about what it means that one candidate — yes, far more than the other — is running a campaign of such epic dishonesty.