Who wins Cain's piece of the pie?

Herman Cain at a South Carolina event 2 December 2011 Image copyright Getty Images
Image caption What will a Herman Cain-sized hole do to the Republican field?

Herman Cain's turn as overnight sensation was already done, but his exit could still be important.

The question is where his supporters go now.

It has been a feature of this Republican race that while Mitt Romney jogs along in first or second place, a series of shooting stars have briefly outshone him before fading and losing their lustre.

Newt Gingrich is not merely the latest "anti-Mitt" candidate. He is the last.

Why? Michele Bachmann or Rick Perry could rise again. Rick Santorum or Jon Huntsman could have their day in the sun.

But I doubt it.

Ron Paul? I am less inclined to rule that out, and I expect him to do well in Iowa.

But I don't see him breaking through to be the main challenger to Romney.

If Cain's voters in the main go for Newt Gingrich, as pollsters think they will, it would be an important and significant boost to the Newt surge.

If they divide up more equally among the rest of the field, it is good for Romney.

Fans of a nomination fight will point to this forced exit as the primary process living up to its purpose.

An unvetted candidate who might have survived a couple of weeks of campaigning couldn't take the strain of this long, drawn-out process.

Better now for Republicans than in the middle of the presidential contest itself.

But it is also true that Cain has been done in by allegations of peccadilloes, ones that he emphatically denies, rather than doubts about his simple-to-remember, more-difficult-to-implement economic plan 9-9-9, or his uncertain grasp of foreign policy.

But this part of the race is at least more about character than policy.