Unseating Obama is a desperately tall order for the entire Republican field; their hopes depend almost entirely on outside events. An economic crisis in the next year could, in theory, create a viable electoral map for Republicans, particularly those whose brand is strong on matters of job-creation or finance – Mitt Romney and Rick Perry, for starters, or even Jon Huntsman if he should somehow win the nomination.

As for Michele Bachmann, her odds are even longer, but not beyond reason if the economy really falls apart; Rolling Stone’s Matt Taibbi described this scenario best, saying that ‘Michele Bachmann has found the flaw in the American Death Star’ (though the thought of the Force being strong with Bachmann, of all people, is too awful to contemplate).

Not so with Palin. The scale of the public catastrophe required to give her a chance to win the presidency would mean that there was no presidency to win – worse than the sundering of the Republic itself, on par with a Biblical plague. As of this week, Palin trails Obama by six points. In Alaska. Her home state. Of such numbers is crushing, laughable defeat made.

The truth about Palin is that she has a small group of extremely devoted fans and struggles to widen her appeal even among Republicans, which, on face, is strange – her conservative credentials are strong. The problem isn’t really her politics (at least among Republicans); it’s her.

John Heilemann and Mark Halperin’s book Game Change describes a focus group conducted by the Obama campaign in the late summer of 2008. One woman in the focus group identified as a Christian conservative, and voiced displeasure that Obama was not born in the US, is a closet Muslim, etc, essentially running through the list of rightwing talk-radio conspiracy theories, but ended by grudgingly declaring her intention to vote for him. When pressed for explanation, she responded, ‘because if he loses, that woman might become president.’

If Palin has this effect on Republicans, it is impossible to conceive of her winning the general election, and almost as unthinkable that she should win the nomination. She has no taste for the hard graft and focus required to campaign, and a candidacy would, in theory, restrict both her and her family’s ability to self-promote with reckless abandon.

Part of the reason she can still command speaking gigs and generate attention for bus tours (even ones she cancels halfway through, an emerging theme in her professional life) is that she is still seen as a potential political player, a media performer who might some day have a position of real power. A run and a (likely disastrous) loss turns her from a potential power into a has-been, a two-time loser, squandering her marketability.

But just because there is no good reason for Sarah Palin to run for president that does not mean she won’t. For years Palin has made decisions that no professional staffer would have suggested or permitted, leading one to believe that she is either advised by fools or simply takes no advice. No doubt the truth is somewhere in between. She may very well be motivated by the mistaken belief that she could win, jealousy at other Republicans getting all the attention, or reasons clear only to her, and decide to run in contravention of all sense.

What would happen if she did? The biggest loser would likely be Bachmann. They share a similar Tea Party, social conservative, anti-establishment base; the prospect of this vote splintering could be enough to tempt Romney back to Iowa, although it would more likely simply mean a lower victory margin for Bachmann. Either way, Bachmann would leave Iowa without a big victory, lose New Hampshire badly, and enter South Carolina with her base still fractured – all good news for Romney.

Palin’s biggest disruption would likely be to the tenor of the debate. Since Bachmann seems determined to tackle this challenge like a professional, the Republican field lacks the cabaret feel that characterised the 2008 primary. Palin could liven things up a bit; she is incapable of maintaining any kind of message discipline, and only a superheroic effort by John McCain’s staff saw her through one debate with Joe Biden in 2008 without serious incident.

This time, there are hundreds of events, no running-mate’s staff to contain her, and a fearsome need to do something dramatic to distinguish herself from Bachmann and other Tea Party-types like Herman Cain. It’s a heady brew indeed; American progressives can only hope she decides to pick up the cup.