The Republican presidential field in the US, which not so long ago just looked like a confused mess, is rapidly sorting itself out. In the space of about a month, four much talked-about prospects have ruled themselves out of contention: Haley Barbour, Mike Huckabee, Donald Trump and most recently Mitch Daniels.

A further prospective candidate, Sarah Palin, has conspicuously failed to make any moves towards running, and most pundits now seem to think she will hold back. And another well-known figure, Newt Gingrich, has run into so much trouble on the campaign trail that his chances -- never great to begin with -- now seem to have pretty much evaporated.