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Herman Cain told members of his campaign staff on Tuesday that he was reassessing whether to proceed with his presidential campaign, an aide confirmed, a day after an Atlanta woman disclosed details of what she said was a 13-year affair with him.

In a morning conference call with his advisers, Mr. Cain said that he would make a decision in the coming days about whether to stay in the race after his campaign was rocked by another round of allegations about his sexual conduct.

The call, which was first reported by National Review, came as Mr. Cain was heading to Michigan for a campaign stop on Tuesday evening. He said that he was discussing the future of his campaign with his family and was considering his options.

“This is cause for reassessment,” Mr. Cain said, according to one participant on the call who spoke on condition of anonymity. “During the summer we had to make some reassessments based on our financial situation. We were able to hang in there.”

Mr. Cain denied the accusations from the Atlanta woman, Ginger White. But he acknowledged that the latest report of sexual misconduct might be more difficult to overcome, considering that the first voting is set to take place in five weeks at the Iowa caucuses. He said that he had not lost his enthusiasm to run, but suggested it was a distraction that could be difficult to recover from.

“With this latest one, we have to do an assessment as to whether or not this is going to create too much of a cloud in some peoples’ minds as to whether or not they should support us going forward,” Mr. Cain said, according to the participant on the call.

Steve Grubbs, the chairman of the Cain campaign in Iowa, urged supporters on Tuesday to not be distracted by the allegations and to press ahead with their effort for the Iowa caucuses.

“I believe in Herman Cain and his ideas. We need to get back on message and make it to the Iowa caucuses,” said Mr. Grubbs, who was on the conference call. “My request is that you don’t let anyone pick your candidate based on these allegations.”

In a message to supporters who have pledged to be precinct leaders for Mr. Cain in Iowa, Mr. Grubbs reminded the Republicans of the “similarly difficult times” in the respective campaign of Senator John McCain and former President Bill Clinton. He noted that Mr. Cain denied the allegations.

“They both weathered the storm and emerged to be their party’s nominees,” Mr. Grubbs wrote Tuesday in his note to supporters. He added, “Thank you for taking a long view of our sometimes challenging electoral process.”

Mr. Cain, whose unconventional and anti-Washington sentiment captured the imagination of Republican voters, has seen his standing in the polls fall over the last month after accusations of sexual harassment surfaced from his time leading the National Restaurant Association. He has denied those allegations, which have been made by at least four women who worked for him.

In an interview broadcast Monday by Fox 5 Atlanta, Ms. White detailed what she said was a 13-year affair with Mr. Cain.

“It was pretty simple,” Ms. White said in the interview. “It wasn’t complicated. I was aware that he was married. And I was also aware I was involved in a very inappropriate situation, relationship.”

The station said that Ms. White produced cellphone bills that included 61 phone calls or text messages to and from a number she said was for Mr. Cain’s private cellphone. When the station sent a text message to the number, Mr. Cain called back and acknowledged knowing Ms. White.

Mr. Cain sought to get ahead of Ms. White’s allegation by making a pre-emptive appearance Monday afternoon on CNN, where he pledged to “stay focused on this campaign.” But several supporters said that they did not see how he could proceed.

“There is no realistic path forward,” said one Republican supporter.

The sentiment on the conference call suggested that Mr. Cain was aware of the gravity of the challenges facing his candidacy. He said that he would wait to see the reaction from his supporters before making a final decision.

“It’s also taken a toll on my wife and family, as you would imagine,” Mr. Cain said at the end of the call, according to National Review. He added, “For some people, you’re guilty until proven innocent. And so, the public will have to decide whether they believe her or whether they believe me. That’s why we’re going to give it time, to see what type of response we get from our supporters.”

Mr. Cain said that he would press ahead with his public schedule, including the speech Tuesday night in Michigan.

As Mr. Cain’s candidacy has floundered, Newt Gingrich, the former House speaker, has seen his prospects rise in recent weeks. If Mr. Cain decides to leave the race, several of his supporters have said that they are likely to support Mr. Gingrich. But with five weeks before the Iowa caucuses, the race remains remarkably unsettled and fluid, making predictions difficult.