Yesterday I noted here that the dust-up over Mitt Romney’s claims about female job loss are premised on a much larger falsehood that is central to Romney’s whole case against Obama.

To wit: Romney has been arguing that the way to judge Obama’s policies is to look at the net number of jobs lost since he took office. But that metric includes the huge amounts of jobs hemorraghed during the months when the economy was in free fall, just after Obama took office — and before those same policies took effect.

Romney has been using this metric for months and months, regularly adjusting the number of net jobs lost on Obama’s watch downward to keep pace with good economic news, with virtually no scrutiny from major news orgs.

Today Steve Benen comes up with the clearest explanation for this fallacy I’ve seen yet:

Imagine you could go back to March 1, 2009, when the global economy was on the brink of collapse. The White House’s Recovery Act had just been signed into law, but the investments had barely even begun, and Obama, still unpacking, did not yet have his full economic team in place.

Then imagine a Republican arguing, just six weeks into Obama’s term, “Mr. President, the economy has lost 726,000 jobs on your watch, and we’re blaming you for the losses.”

Would any serious person find this fair or reasonable? Of course not. And yet, it’s the basis for the Romney campaign’s entire economic critique of the Obama administration.

....if we start the clock on March 1, 2009, after Obama’s first full month in office, the net change for his presidency is -102,000 (or +484,000 looking only at the private sector).

If we say Obama walked into a nightmare and the first six months of 2009 shouldn’t count against him, the economy, combining all the jobs lost and all the jobs gained, had added 2.24 million overall (2.8 million looking only at the private sector).

When we start counting makes all the difference. To make Obama look like a “failure,” Republicans want the earliest possible point to start the clock.

Exactly. One of the central premises of Romney’s entire case against Obama is completely ridiculous. Yet aside from a few pointy-headed fact checkers, no media figures are writing about it or questioning it. If I ruled our media universe, every reporter and commentator writing about this campaign would look at the chart Steve has drawn up illustrating the point. Politico’s Ben White is also good on the topic today.

By the way, it may soon get harder and harder for Romney’s mega-distortion to escape notice for much longer. Here’s why: If the recovery doesn’t sputter — which is anything but assured — the next positive jobs report may mean that even the net jobs gained/lost number Romney uses will slip into positive territory, if you start the clock in February, the first month after Obama took office.

At that point, if Romney continues to argue that this metric proves Obama’s policies failed, his case will have to undergo some serious scrutiny. Right?