(CNN) -- Embattled Republican presidential candidate Herman Cain told his staff Tuesday he is "reassessing" the viability of his campaign in the wake of an allegation made Monday that he engaged in an extramarital affair that lasted for more than 13 years, CNN has learned.
A top campaign source told CNN he expects a decision "within a few days," based on whether Cain's fund-raising dries up.
Another source familiar with internal campaign deliberations told CNN the question now is "money and support." The source, speaking on condition of anonymity, said the already small campaign operation would likely have to lay off some staffers.
"We just staffed up some, but at a minimum it looks like (there is) no choice but to staff down," the source said. "We are in the period of the campaign where we need to spend to perform, and the question is will donors and Republicans believe" Cain or his newest accuser.
Cain spoke Tuesday morning to his staff for about 10 minutes. He said during the meeting that allegations of sexual impropriety "are taking an emotional toll on his family and that this is a very difficult time," said Cain's Iowa chairman, Steve Grubbs.
But on Tuesday night, the candidate went forward with a 40-minute speech to an enthusiastic audience at Hillsdale College in Hillsdale, Michigan. In it, Cain made no reference to the assertion by Atlanta businesswoman Ginger White that she and Cain carried on an on-again, off-again affair for more than 13 years before it ended about eight months ago.
Cain denied her assertion on Monday night and, on Tuesday, he repeated the denial in a letter to supporters. "I am writing you today to assure you that this woman's story is completely false," he wrote.
"I do know Ms. White. I have helped her financially at times over the past few years, just as I have helped many friends and acquaintances throughout the years. I thought Ms. White was a friend in need of a supportive hand to better her life.
"Ms. White has made it apparent that she was abusing the friendship."
The story broke Monday night when Atlanta television station WAGA aired an interview with White in which she said she that the affair began after she and Cain met in the late 1990s in Louisville, Kentucky, where Cain was giving a talk as head of the National Restaurant Association.
"I was aware that he was married, and I was also aware that I was involved in a very inappropriate situation -- relationship," she said.
White told CNN affiliate WSB that she had and Cain had a sexual relationship. "Absolutely," White said when asked if the relationship was sexual.
White told WAGA the affair ended early this year as Cain prepared to announce his presidential bid. But she pointed to mobile phone records she said prove Cain was calling her as late as September, including one call at 4:26 a.m.
Cain, who lives in suburban Atlanta, told his staff Tuesday that White was "a friend and he helped her financially but that nothing inappropriate took place."
The candidate said his wife's reaction upon hearing of the accusation was, "Here we go again." And he said he had no plans to drop out of the race.
"Not as long as my wife is behind me and as long as my wife believes I should stay in this race," he said.
In a written statement issued Monday, after the interview aired, Cain said, "I am running for president of the United States of America, and the reality is that there are individuals out there that favor the status quo of higher taxes, more government and political cronyism and they are afraid of a Cain presidency."
White's emergence comes after two other women -- Sharon Bialek and Karen Kraushaar -- accused Cain this month of sexually harassing them in the 1990s while he was head of the restaurant association. Two other women also have said Cain sexually harassed them while they worked at the association, but they have declined to be identified.
Cain has denied all the accusations, but he has slipped in published polls since the allegations surfaced.
Cain attorney Lin Wood said Monday that reporters had no business asking about the allegation.
"Some things are fair game and some aren't," Wood told CNN in a telephone interview, adding that this was one that was off-limits. "You've got to draw the line somewhere."
WAGA said it and other news organizations had received a tip from someone who knew White about the alleged affair.
"I wanted to come out and give my side before it was thrown out there and made to be something, you know, filthy, which some people will look at this and say, that's exactly what it is," White told the station.
WAGA said White's history includes a 2001 sexual harassment claim against an employer that was settled, a 23-year-old bankruptcy in Kentucky and several evictions over the past six years. A former business partner accused her of stalking her with repeated e-mails and texts in a case that was ultimately dismissed, followed by a libel suit White lost because she failed to respond to it, WAGA said.
But White's attorney, Edward Buckley, told CNN's "John King USA" that his client has no apparent financial motive for making the accusation and "everything to lose."
"To tell you candidly, I don't know if she is employed or not, because she was kind of on the ropes because of all this stuff," Buckley said. "The media called her employer before this story came out, and it made it very difficult for her in the workplace."
CNN's David Mattingly, Alan Silverleib, and Tom Watkins contributed to this report.