Why isn’t Mitt Romney winning by now, given the painful sluggishness of the recovery, upside-down right-track-wrong-track numbers, and Obama’s high disapproval on the economy?

For many analysts, that’s the key question. Charlie Cook has decided Romney is not leading because he failed to develop a positive vision of himself. Sean Trende, meanwhile, says the answer is that the economy isn’t as bad as it was in 1980, or even in 2008.

Here’s my own unscientific answer. It’s grounded in a nuance I believe is central to the Obama campaign’s understanding of the race: The distinction between whether voters have decided Obama has failed, or whether they have decided he has merely disappointed them by falling short of expectations, an outcome these voters have come to see as understandable, given the circumstances.

Republicans will scoff at this distinction. To them, the idea that voters have decided Obama is an abject failure is as self-evident as the color of the sky. One GOP strategist captured this well: “If you’re just telling people that Obama doesn’t know what he’s doing, you’re not telling them anything they don’t already know.”

But this may reflect what Jonathan Bernstein has described as the “conservative closed information feedback loop,” in which the widespread presumption that swing voters see Obama in the same terms conservatives do precludes a clear-eyed assement of real voter perceptions. To be clear, undecided voters may still end up deciding Obama’s failure is sufficiently evident that it merits casting him out. But it’s not clear they have decided he failed yet, and dismissing this as a factor misses what may be the real reason the economy has yet to doom Obama — and why he may be able to prevail in spite of it.

Republicans often acknowledge that voters appreciate the scale of the mess Obama inherited. But they quickly rejoin that what matters is how he responded to it, and therein lies his “extraordinary record of failure,” as Romney has put it. But if undecided voters don’t see things this way, and instead believe Obama has disappointed them for somewhat understandable reasons, this should change how we think about the race.

Here’s why: It’s very plausible that in spite of their own disappointment, voters have adjusted their expectations downward as to what presidents can do for this economy as they came to appreciate the magnitude of the crisis. This came up again and again in conversations that Ron Brownstein, Matthew Dowd, and yours truly had with undecided voters. These voters are unhappy with Obama. But they have not yet decided Obama’s approach is discredited. Their declining expectations have left them open to the argument that even if they disapprove of the current economy under Obama, Romney doesn’t have the answer either, and that Obama's approach still has a better chance of bearing fruit over time.

Indeed, it’s not clear either candidate has won the argument about the economy. In the latest Post poll, Romney holds a seven point advantage on the generic question of who should be trusted on the economy. But it also finds that the two are tied on which man’s election will result in an improved economy. Forty three percent say they are confident the economy will get on track of Obama is reelected; 56 percent say they are not. The numbers for Romney? A virtually identical 43-55. And a majority says spending more on infrastructure, rather than cutting taxes, is the way to create jobs, 52-33. Public opinion is conflicted and in flux; expectations have been revised downward; no one has won the argument about the way forward yet.

If these voters had decided Obama’s approach has been discredited, they’d be willing to change course pretty much no matter what. But they just aren’t there yet. And this may be the key reason why Romney hasn’t taken the lead. Failing to appreciate this nuance — and operating from the assumption voters think Obama is an abject failure — could prove a miscalculation. It could lead Romney to overestimate voter disagreement with Obama’s ideas and vision; to imagine he needs to do less to articulate an alternative vision of his own; to underestimate Obama’s chances of fighting him to a draw on the economy; and to downplay the importance other issues — as well as the tattered GOP brand — could have at the margins if Obama does manage that.

I don’t have scientific proof this is how undecided voters widely see the race, which remains a toss up. But I believe this theory is central to the Obama campaign’s view of things, on how to close this out, and on why he could still survive.