Two new developments this week in the race for next year’s Republican presidential nomination. First, Mitt Romney joined the list of semi-declared candidates by “setting up an exploratory committee”, becoming the second serious contender to do so after former Minnesota governor Tim Pawlenty.

But this was rather overshadowed by the other development: a CNN opinion poll that put billionaire Donald Trump equal at the top of the field for the nomination. Romney, long considered the front-runner, could manage only equal fourth. Here are the numbers:

Mike Huckabee 19%
Donald Trump 19%
Sarah Palin 12%
Newt Gingrich 11%
Mitt Romney 11%
Ron Paul 7%
Michele Bachmann 5%
Mitch Daniels 3%
Tim Pawlenty 2%

With almost nine months to go before the first votes will be cast, you can’t expect polling at this stage to be very informative. All the same, the fact that a controversial real estate mogul who has never held public office, and whose campaign so far has been pitched to the “birthers” (the conspiracy theorists who claim Barack Obama is not a natural-born US citizen), could do so well is quite remarkable.

Few commentators think that Trump, if he runs, would be a serious chance. For a guide to expectations, as distinct from voter preferences, consider the latest prices on the Intrade betting market this morning:

Romney 26.0
Pawlenty 15.5
Daniels 9.3
Bachmann 6.9
Huckabee 5.6
Trump 7.5
Jon Huntsman 5.5
Palin 4.8
Haley Barbour 3.8
Gingrich 3.5
Paul 2.0

(Strictly speaking these are not percentages, since with the also-rans included they add to about 103, but they’re close enough for comparison purposes.)

The contrast is striking: the two leaders in the poll are only mid-field in the prediction market, and two of the latter’s three front runners scored at the bottom of the poll. It looks as if there’s a serious disconnect between what Republicans say they want and what they’re expected to actually get.

What’s going on becomes clearer if we divide the field into mainstream candidates and crazies — an admittedly subjective process. CNN puts mainstream support (Romney, Daniels and Pawlenty) at just 16%, against 73% for the crazies. But Intrade gives the mainstreamers (including Huntsman) 54.6 of a chance between them and the crazies only 34.1.

With nothing actually at stake so far, significant numbers of Republican voters are using the polls to vent their frustrations or give reign to their wilder fancies. But pundits expect that when the choice is upon them next year, enough of them will return to planet Earth to put the nomination into safer hands. But will they?

Romney is the candidate with most to lose here. Low poll numbers for Pawlenty and Daniels can be explained by poor name recognition, but Romney — who ended up about equal second with Huckabee in the 2008 race — has no such problem. The GOP base knows him, but they don’t much like him.

Two reasons are commonly given: the fact that he’s a Mormon, which raises suspicions among evangelicals, and the fact that as Governor of Massachusetts his record was quite moderate — including the introduction of a universal health care plan strikingly similar to that passed last year by the Obama administration, which is a prime attack target for Republicans.

I’m sceptical of the first of these, since I’m yet to see any evidence that America’s fundamentalists actually care about theology, but a general impression of religious oddness might be holding him back slightly. The second, however, is real political trouble, and Romney so far seems unsure how to deal with it.

You can’t expect to win in Massachusetts as a conservative Republican, so it’s not surprising that Romney adopted some different positions there to what he now professes or even to what he really believes. That needn’t be fatal; Scott Brown, who won a senate seat there last year, took a similarly moderate stance, but that didn’t prevent him becoming a hero to the Tea Partiers.

Romney’s problem is that he seems unable to project sincerity: his explanations for why he’s changed his mind, or why what looks like a change really isn’t, are unconvincing, almost as if his heart isn’t quite in it. In a field of strong personalities he comes across as a drifter, almost colourless.

But Republican candidates have overcome serious image problems before — most obviously John McCain, who also alienated many conservatives and was just about written off in late 2007. If Republican voters insist on voting their passions, Romney probably won’t have much of a show. But if realism takes hold of them over the next few months, he still looks better qualified than his rivals.