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Republican Herman Cain successfully fought a week's worth of sexual harassment allegations in part because his accusers stayed silent.

That changed Monday, when a former employee described an encounter with Cain so tawdry and aggressive it greatly increased the challenge the businessman faces in winning the presidential nomination of a conservative, family-values party.

"I am coming forward now to give a face and a voice to those women who cannot or do not wish to come forward," Sharon Bialek said at a nationally televised news conference organized by her attorney, Gloria Allred. In vivid detail, the middle-aged single mother said Cain had put his hand up her skirt and pushed her head toward his crotch while she visited him seeking job advice in 1997 when he was head of the National Restaurant Association.

Cain's campaign issued a statement calling any claim against him to be "completely false."

Later, in a fundraising email to supporters, Cain wrote: "I held various executive positions in corporate America for several decades. I had thousands of employees working for me. I can't even begin to recall how many conversations I had with people during that time, how many directives I gave, how much friendly banter might have taken place.

The comment was similar to what he's said — and what his supporters have seemed to accept — since the first decade-old allegations of sexual harassment surfaced on Oct. 30.

But now, facing a flesh and blood accuser with very specific and vulgar allegations, Cain could find himself with less room to maneuver as he seeks to overcome this controversy and win the White House.

Cain's unconventional candidacy had long seemed resistant to the normal laws of political gravity.

The motivational speaker and former chief executive of Godfather's Pizza was dismissed as a gadfly at first, but his humor and strong conservative credentials charmed Republicans looking for an alternative to Romney even as Cain continued to trail in fundraising and had no discernible campaign operation in key early states.

When the sexual harassment allegations first surfaced, Cain took to the airwaves to defend himself but ended up giving conflicting answers to questions.

He acknowledged the trade group had made a cash payout to one accuser after denying any money had changed hands. The trade association confirmed that it had reached a monetary settlement with a woman and had released her from a confidentiality agreement she had signed. The woman's lawyer, Joel Bennett, announced late last week his client had decided not to speak publicly.

Throughout the week, Cain and his allies blamed others for the controversy — the news media, Republican rival Rick Perry and liberals supposedly threatened by a conservative black man's success. The absence of names and specific allegations about what Cain was said to have done allowed him to cast himself a victim of an unfair "witch hunt."

His strategy seemed to work at first, with several polls suggesting Cain's position atop the field of GOP primary contenders remained strong.

A new USA Today/Gallup poll taken before Bialek stepped forward showed Cain and top rival Mitt Romney tied at 21 percent support. The poll showed a 53 percent of Republicans thought the charges against Cain were not true.

Then came Bialek, a Chicago-area woman Allred said was a registered Republican with no political motive to bring Cain down. Terminated from her job as a fundraiser for the NRA foundation, she said she reached out to Cain for help getting her job back or finding new work.

Her encounter with Cain took place in a car, Bialek said. She said she was embarrassed by what happened and had never pressed charges.

Bialek said she had decided to go public only after learning other women had had similar encounters with Cain.

"We need a leader who can set an example which exemplifies the standard of a person of good moral character. Mr. Cain, I implore you: Make this right," Bialek said.

To be sure, not everyone was buying Bialek's allegations.

"I don't believe that for a minute," said Debbie Dooley, a leader of the Atlanta Tea Party Patriots and a Cain supporter. "I think it's a case where someone has a scorched earth grudge against Herman Cain because they're afraid of him."

Some have also cast doubts on Bialek's association with Allred, a well-known celebrity feminist who has long sought the spotlight. The two women are already booked on several television news programs to further discuss Bialek's accusations.

But Dave Welch, a GOP strategist unaligned with any candidate, said the prospects for Cain's candidacy were bad and getting worse.

"I think it's a disqualifier, but people are saying, 'This was so long ago,'" Welch said. "Yes, it was a decade ago and the base doesn't want to believe it. But these are very serious."

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Associated Press riter Philip Elliott in Washington and Shannon McCaffrey in Atlanta contributed to this report.

Follow Beth Fouhy on Twitter at www.twitter.com/bfouhy