As a fifth woman accuses him of sexual impropriety -- not of harassment this time, but of a 13-year extramarital affair -- Herman Cain is reassessing his presidential campaign, according to senior staff members who held a conference call with the embattled candidate on Tuesday.

It is becoming increasingly clear that, while the allegations against Cain remain unproven, they have devastated a campaign that was already struggling to build on-the-ground infrastructure and an authoritative image. At this point, there is a growing consensus, with Ginger White's claim that she and Cain had a 13-year affair, that Cain's presidential hopes are all but shot.

Herman Cain was never a credible candidate for president of the United States, because he does not have the background or the knowledge to be a credible candidate, Whit Ayres, a Republican political consultant, told IBTimes, referring to Cain's lack of political experience and his well-publicized foreign policy gaffes. These latest allegations eliminated whatever slim chance he ever had to be the Republican nominee.

Even before White went public with her allegations, Cain's support had fallen by more than half from an October Quinnipiac poll (30 percent) to a November Quinnipiac poll (14 percent). The November poll showed him in a distant third place behind Newt Gingrich and Mitt Romney, and it seems unlikely that he will escape without further damage now.

A More Substantiated Claim

Since Politico first reported on the 1990s harassment complaints against Cain on Oct. 30, it has seemed that voters care little about allegations that can be easily denied.

When the story consisted of two anonymous women who had received settlements more than a decade ago, and Cain denied any wrongdoing and said the complaints had been found to be baseless, most of his supporters gave him the benefit of the doubt. His support remained relatively steady, his fundraising actually increased, and 70 percent of Republican voters told pollsters that the allegations would not affect their vote.

But then two more accusers surfaced, and one of them, Sharon Bialek, came forward with her name, face and a detailed story. She had asked Cain for help finding a new job after she was fired in 1997, and she claimed that one night, after dinner, he drove her to the National Restaurant Association headquarters in Washington, D.C., reached up her skirt, and pulled her head toward his crotch. She said that when she protested, he responded, You want a job, right?

The same day Bialek held her press conference, Karen Kraushaar, one of the two women who had received settlements in the 1990s, went public as well. Now there were two names and faces attached to the allegations, and those allegations were more specific than the nebulous term harassment -- and while Cain continued to deny any wrongdoing, his poll numbers began to drop. Clearly, with more details out in the open, voters saw the allegations as more believable than they had before.

It stands to reason, then, that the newest accusation will have a measurable impact on Cain's support because it, too, involves a name and a face. More importantly, while Bialek's and Kraushaar's stories were essentially he said, she said, White has evidence to back up her claim that she and Cain had an affair.

White showed Fox 5 News phone bills listing 61 calls and text messages from Cain's personal cell phone over the course of four months, some with time stamps earlier than 5 a.m. (Cain responded that he only contacted her because he had been giving her financial support.) Her statement that Cain flew her to various cities where he was speaking can also be confirmed or disproven in the coming weeks by looking at airline purchase records.

If airline records do, in fact, confirm that Cain bought tickets for White, and if the travel dates coincide with his own speaking engagements, it will be lights out for his campaign.

Growing Inconsistencies

Even before White came forward, new evidence had begun to cast doubt on some of Cain's denials.

In response to reports that Kraushaar had been given a large settlement to leave the National Restaurant Association and not talk about the sexual harassment complaint she had filed, Cain told Fox News that Kraushaar had actually been fired because her job performance was not up to par.

But Maria Cardona, Kraushaar's supervisor at a subsequent job at the Immigration and Naturalization Service, told CNN that Kraushaar was one of the hardest-working individuals I have ever known and said that her credibility was beyond reproach.

In response to Bialek's press conference, in which she accused Cain of trying to grope her, he said, I don't even know who this woman is. ... I didn't recognize the face, I didn't recognize the name, nor the voice.

But Amy Jacobson, a Chicago radio host who attended a Tea Party rally in September at which both Cain and Bialek were present, said she had seen them talking there. She was inches from his ear, Jacobson told The Chicago Sun-Times, and he was saying to her, Uh-huh, uh-huh. That squares with Bialek's statement that she had approached Cain at the rally and asked him if he remembered her, and that he had said yes.

None of this is proof that Cain is guilty of the allegations against him, but every time his statements clash with other sources' statements, he loses a little more credibility in voters' eyes -- and that, much more than the allegations themselves, is what has sunk his campaign.

These charges, in and of themselves, aren't enough to do in a candidate nowadays, Brian Kirwin, a political consultant for Rourk Public Relations, told IBTimes earlier this month, before Bialek and Kraushaar went public. The issue of harassment is almost superseded by the issue of his personal honesty. If a first-person, detailed account comes out, even if it's a he-said-she-said -- if that puts a big question mark on Herman Cain's honesty, he's finished. Republicans have very little tolerance for that, especially in primaries.

In the weeks since, that is exactly what has happened.

A Matter of Public Concern

In addition to denying White's allegations, Cain's lawyer argued on Monday that the public has no business looking into his client's private sexual life to begin with.

Cain will not discuss the accusations even if his principled position is viewed unfavorably by members of the media, lawyer Lin Wood said in a statement to Fox 5 News. This is not an accusation of harassment in the workplace -- this is not an accusation of an assault -- which are subject matters of legitimate inquiry to a political candidate. Rather, this appears to be an accusation of private, alleged consensual conduct between adults -- a subject matter which is not a proper subject of inquiry by the media or the public.

In theory, that is true -- as White's allegations do not involve illegal behavior, Cain is not obligated to account for whatever consensual sexual activity may or may not have happened. But it is naïve to think that, on the national campaign trail, people will stop asking questions just because they don't have to be answered.

A lot has changed since the 1960s, when the media gave John F. Kennedy a free pass on his suspected extramarital affairs because they were not considered relevant to his performance as president. Today, in the age of family-values voters, what candidates do in the bedroom, consensual or not, is frequently made a matter of public concern.

Many voters, especially the socially conservative voters who made up a large part of Cain's support base, care about character as much as they care about policies, and so, for better or for worse, candidates are judged for their personal indiscretions. In terms of public opinion, it almost doesn't matter whether an allegation is true. If it seems plausible, enough people will believe it to have an effect on the candidate's popularity.

The accusations may indeed be false, but if agreements were signed, something happened, even if it wasn't harassment, Ronn Torossian, the CEO of 5W Public Relations, told IBTimes earlier this month. He seems to think that because he tells somebody not to talk about it, it'll go away. It's not going to go away.

It hasn't gone away, and it still won't.

Has the Cain Train Derailed?

Sometimes politicians do survive sex scandals unscathed. Just look at U.S. Rep. Barney Frank, D-Mass., who admitted in 1989 to having an affair with a male prostitute but was re-elected the following year.

Usually, though, even if they do recover eventually, their popularity suffers in the short term.

Bill Clinton has rebuilt his reputation very successfully since the Monica Lewinsky scandal, but if he had been up for re-election in 1998, he would probably have lost. Sen. David Vitter, R-La., admitted to using an escort service in 2007 and kept his career, but he had three years to regroup before he had to run for re-election in 2010. Newt Gingrich had an affair with a congressional aide while he was speaker of the House in the 1990s, and that, coupled with the House sanctioning him for ethics violations in 1997, made him a political pariah until very recently.

Cain doesn't have that sort of time, and his decision to reassess his campaign prospects shows that he realizes how serious the situation is.

In the circus that is American electoral politics, it would be foolish to count Cain out entirely. Stranger things have happened, as even Newt Gingrich -- probably the Republican candidate who stands to gain the most if Cain drops out of the race -- noted.

Remember, I was supposed to be dead in June and July. I am not going to go around declaring anybody else dead, Gingrich told CBS News on Tuesday. I think any candidate has the right to try to recover. They have the right to try to get back in the game.

But if Cain chooses to try, it will be an extremely tough road.