Some presidential election campaigns will end here in South Carolina.

The candidate or candidates will come to the realisation that they cannot win the Republican nomination, that their vision of America has not been accepted by the majority, and that despite the hopes and dreams, the hands shaken and the interviews given, that it is finally over.

Jon Huntsman has already left the field, lacking money and supporters, his “ticket out of New Hampshire" not even good for a week.

To accept the thinking of the Mitt Romney campaign, then the contest is over.

He has done what no other Republican challenger has, and that's win the first two nomination contests, in Iowa and New Hampshire. And they argue, victory in South Carolina on Saturday - which has picked the winner in every contest since 1980 - will make him the presumptive nominee for his party. They are attempting to build an aura of inevitability.

The conservatives in his party don't like him.

They have examined his record as Governor of Massachusetts and they see him as too moderate, too liberal and certainly not in line with their thinking and philosophy.

They cite his past support of abortion rights and the passage of a health care system which closely resembles the national health care law pushed through by Barack Obama and is despised by large swathes of the Republican Party.

There is a feeling he adopts positions which are more likely to win voter support, that test well with focus groups rather than ones driven by a deeply held philosophy.  As a new book on Romney puts it: “strategy triumphs ideology”.

But for months, Romney has been the man to beat because the conservatives can't rally around a standard bearer.

He has watched candidates flare and fade, and in South Carolina he faces three challengers who claim they are more conservative than him, more in tune with the base than him, and as a result are likely to split the right wing vote and hand him a win.

Rick Perry - the gaffe-prone Texas governor - on the night he finished fifth in Iowa said he was taking time to rethink his campaign.

It seemed to be shorthand for walking away, but his backers appeared to have other ideas and urged him to take one last run in South Carolina. He's on course to finish last and will almost certainly step out if that's the case. But he will attract conservative support which could have gone elsewhere.

Rick Santorum and Newt Gingrich remain the last two 'big dogs' of the right and will each attract substantial backing.

No one candidate ticks all the boxes for the right. And while that wing of the party has been casting around looking for ‘Not Mitt Romney’, the split field has driven him into a commanding position.

One single right-wing candidate could have pushed Romney until the end, changed the face of this contest and given his campaign manager a few more sleepless nights.

In their desperation to drag down the frontrunner, to get people to switch allegiances the ‘big dogs’ have growled and attacked, citing Romney’s time with an investment firm.

They say he laid off workers in companies he took over, slashed jobs and ruined lives to make himself rich.

Members of the party have been angry with the tone of the debate, fearing it has simply handed Democrats a huge arsenal of sound bites to be re-used and repeated in the summer.

And despite it all, the latest polls show Romney is still likely to be the man who will face Obama in November's general election.

Large parts of the Republican Party have never loved Romney. To win, he has to convince those who are fighting against him so strongly at the moment to unite in the desire and fight to replace Obama.

He will be hoping that it is true what they say that Democrats fall in love with their candidate - Republicans fall in line.