Either he's the Great Survivor, or this could be the beginning of the end of Herman Cain's unlikely campaign for the Presidency of the United States.

Thus far, the former pizza mogul has managed to coast a series of gaffes and scandals that would have felled most candidates. Now, there's a debate over whether these latest allegations of sexual harassment could prove a tipping point for the campaign that's surprised everyone who thought they could predict how the Republican race would turn out.

Look at the numbers, and Cain appears to be in a pretty comfortable position. The latest poll of polls from Real Clear Politics puts him at 25 per cent; ahead of Mitt Romney on 23. And that's after what must have been the worst week of his political life.

The reason is partly Cain's unashamed populism, coupled with his traditional conservative values that appeal so much to the Tea Party-kind of politics that has become mainstream Republicanism across much of the country.

As John Cassidy writes in the New Yorker, Cain -- more than anyone else in the GOP field -- has discovered a way of connecting with all those disillusioned Americans, fearful about the future and longing not for doom-mongering, but optimism. The businessman who proclaims himself a "problem solver, not a politician" sounds a surer bet than someone mired in the old-style partisan bickering which has given Washington such a bad name.

TA Frank, who profiles Cain for the upcoming edition of the New York Times Magazine, depicts a candidate who just seems to plough on regardless. Former staff members, he writes, describe him as a man with

zero interest in policy. They speak of events canceled at the last minute to accommodate any available television interview. They speak of unrelenting self-absorption, even by the standards of a politician. But they don't speak of someone who can't win.

So far, at least, this winning streak has kept Cain's supporters on his side -- prepared to carry on giving him the benefit of the doubt. But how long can that go on, as more women come forward, prepared to go on the record with their claims of sexual harassment? Surely daily press conferences denying scandals do not a Presidential candidate make?

Last night Cain gave his first real press conference on the subject, allowing reporters to ask questions -- then appearing on ABC, to reject the latest allegations from two women, Sharon Bialek and Karen Kraushaar, and insist that it wouldn't derail his campaign.

He brought along his very own celebrity attorney, claimed he was doing it all "for the children" and denied everything, point blank. "I can categorically say I have never acted inappropriately with anyone. Period." he said. Once again, he blamed the media and something he called the "Democratic Machine" for drumming it all up in the first place.

But tonight, as the GOP candidates meet for their 10th debate in Michigan, it's a crucial moment for Cain. His performance tonight could determine whether he can draw a line under the sexual harassment allegations and start talking about something else. It's a moment for his supporters to decide if they're justified in staying loyal. Or, Herman Cain could turn out to be just another maverick candidate whose novelty and hubris proves unable to stay the course.

Felicity Spector is a senior producer at Channel 4 News.