It began on August 7. The Romney campaign launched a major offensive on welfare policy, accusing President Obama of "gutting" existing law and "dropping work requirements."

The attack was as obvious a lie as has ever been spoken by a presidential candidate. Mitt Romney had made this up, but proceeded to repeat the lie in every stump speech, and in five separate ads released over the course of two weeks. This one, racially-charged, entirely-made-up claim had quickly become the centerpiece of the entire Republican campaign.

And then something interesting happened. It disappeared.

Sahil Kapur reported the other day that Romney, in his convention address, chose not to repeat the lie, and the claim wasn't included in Paul Ryan's convention speech, either. When I checked the transcripts for Chris Christie, Marco Rubio, Condoleezza Rice, and Jeb Bush, not one of them made even the slightest reference to the welfare lie.

But wait, there's more. Romney has given three speeches since his convention address, delivering remarks in Lakeland, Jacksonville, and Cincinnati. The combined total of references to welfare in those speeches? Zero.

Also, I spoke this morning with a Democratic source who confirmed that the Romney campaign's television ad featuring the welfare lie is not currently on the air.

So, over the course of about a week, this one transparent falsehood went from being the most potent attack in the Republican arsenal to a lie Romney and his team suddenly didn't want to repeat.

What happened? For now, we can only speculate -- the campaign has not explained the shift -- but I wonder whether the allegations of racism started to take a toll.

Not only had every independent analysis proven that Romney was blatantly lying, but there was a growing consensus that the Republican was deliberately trying to exploit racism to advance his ambitions.

On Wednesday, the day before Romney's speech, National Journal's Ron Fournier wrote a lengthy piece making clear that the GOP candidate has been playing a carefully-crafted racial game, and given Fournier's credibility with the political establishment, his analysis was widely noticed, and raised questions anew about how far the former governor would go to base his campaign on an ugly, divisive deception.

It's quite possible Romney found it easier to switch to other falsehoods, rather than risk alienating the American mainstream by sticking with his racist lie.

Or maybe I have this backwards and this is merely the eye of the storm. Romney will reportedly launch its next round of ad buys tomorrow, and maybe the welfare lie will be up front and center once again. As of today, however, the absence of the lie is hard to miss, given how invested Republicans were in the false accusation a week ago.