It looks as if Christmas has come early for Barack Obama this week. Newt Gingrich, former speaker of the house of representatives and probably one of the most disliked and distrusted men in American politics, has shot to the head of the pack in the race for the Republican presidential nomination.

The rolling average of opinion polls at RealClearPolitics  has Gingrich six points clear of Mitt Romney, 26.6% to 20.4%, and eight points ahead in Iowa, the first state to vote in just over a month. The betting market still prices Romney ahead, but only narrowly; he is now less than even money where only a fortnight ago he was at 2/1 on.

The big news recently has been the implosion of Herman Cain’s campaign.

Already plagued by allegations of s-xual harassment, Cain now has to contend with a woman named Ginger White who claims to have had a 13-year affair with him, ending less than a year ago. Cain’s denials of the affair have sounded half-hearted and unconvincing, and he says he is “reassessing” his campaign and will decide next week whether to persevere.

Cain had already been written off by most pundits, but if — as seems likely — his campaign is wound up in the near future it will be a big boost for Gingrich, since his candidacy is pitched to the same sort of voters. Although Gingrich certainly has his own negatives, there’s not much doubt that most of Cain’s supporters will rally to him rather than back Romney.

To some extent this is just a continuation of the process that’s been going on for months, of a succession of anti-Romney candidates ballooning in the polls, coming under scrutiny, being found wanting and rapidly fading, to be replaced in turn by a new flavour of the month.

Donald Trump, Michelle Bachmann, Rick Perry and Cain have all gone through this cycle; now, it seems, it’s Gingrich’s turn.

The difference, however, is that there’s not much time left: the cycle can’t go on forever, not just because the GOP would eventually run out of candidates but because actual voting starts happening. It looks as if Gingrich may be the lucky one who peaks at the right time.

And although Gingrich may be poison with the electorate at large — Paul Krugman quipped that “he’s a stupid man’s idea of what a smart person sounds like” — he clearly has real strengths.

Nate Silver last week pointed to a poll showing Gingrich way ahead of the Republican field on the question of who has “the knowledge and experience necessary to be a good president”. Silver’s interpretation was that while Romney’s supporters go for Romney on that question, the anti-Romney voters tend to converge on Gingrich — much more than they do with respect to voting intention:

“But if you want to make Mr Gingrich look worldly, experienced and presidential, that’s going to be a lot easier when you put him on a stage with candidates like Mr Cain and Mrs Bachmann. A lot of Mr Gingrich’s current support, I suspect, comes from voters who had once been inclined to support an outsider like Mr Cain or Mrs Bachmann or even Donald Trump — but who got tired of hearing about how they weren’t cut out for the job or developed some of those concerns themselves.”

Australian observers of this circus need to put out of their minds any thought of preferential voting. If this were an Australian election, it wouldn’t matter much how many anti-Romney candidates there were; whichever one of them came out ahead would scoop up the preferences of the rest and comfortably overtake Romney. But American elections are first-past-the-post, so splitting the vote among several like-minded candidates can be fatal.

Ever since, early this year, it became likely that Sarah Palin wouldn’t run, I’ve been confident that Romney would be the nominee. While I still think that’s more likely than not, there’s now a clear possibility of a single candidate being able to harness the anti-Romney vote in enough strength early enough to go on and win. The Democrats must be salivating at the prospect.

The other possible beneficiary is former Utah governor Jon Huntsman, regarded as the most moderate candidate in the field. Unlike the others, Huntsman is not seriously contesting Iowa but is focusing on Romney’s home turf of New Hampshire, where his poll numbers have shown modest gains. His strategy depends on Romney being badly beaten in the early primaries, so that the party establishment will abandon him and rally behind Huntsman as the only sane candidate remaining.

That’s still a long shot, but it’s looking a little more plausible this week.