WASHINGTON -- Herman Cain vowed to "reassess" his presidential campaign and prominent backers started to rethink their support Tuesday following a Dunwoody woman's claim of a lengthy extramarital affair with the candidate.

The McDonough resident who a month ago was the shooting star of the Republican race went on with a foreign policy speech in Michigan in which he did not address the controversy, but the turmoil of recent weeks had clearly taken its toll.

In a conference call with staff, Cain said that he will press on and continued to "deny unequivocally" that he engaged in a consensual 13-year relationship with Ginger White.

"We’re going to continue until we complete our assessment over the next several days," Cain said, according to reports from the National Review and Des Moines (Iowa) Register. "But if a decision is made, different than to plow ahead, you all will be the first to know."

Atlanta radio host Neal Boortz, a friend of Cain, said the candidate should consider gearing down his campaign to concentrate on his family because White's allegation may have dealt his presidential chances a fatal blow.

"It probably pretty much puts a fork in Herman Cain’s chances of winning the GOP nomination," Boortz said on his Tuesday show. "True or not, it does that. It may be rapidly approaching the time for Herman Cain to concentrate on his relationship with his family, and try to get through this thing."

Boortz, whose political talk show airs on AM 750 and 95.5FM News/Talk WSB, defended Cain during allegations of sexual harassment that surfaced recently from Cain's time heading the National Restaurant Association in the 1990s.

But this claim was hurting Cain in a way that the earlier accusations of sexual harassment did not because of the appearance of dishonesty, said Debbie Dooley, a co-founder of the Atlanta Tea Party. She cited records of 61 calls and texts between Cain and White and contrasting statements by Cain -- who strongly denies the affair -- and his lawyer, who did not.

“Activists are sick and tired of the same old politicians” who say one thing and do another, said Dooley. “They want honesty.  That’s one of the things that attracted activists to Herman Cain, they thought he was outspoken, forthright and honest.”

Another one of Cain’s top Georgia supporters, state Sen. Josh McKoon, R-Columbus, refused to comment Tuesday when contacted by the AJC. But when a Chicago woman earlier this month claimed Cain groped her in 1997, McKoon was quick to defend Cain.

The response was telling for Larry Sabato, the head of the University of Virginia Center for Politics.

"I was struck by how few Cain defenders there were, compared to the time of the earlier allegations." Sabato wrote in an email. "In fact, many Republicans were bemoaning the fall of their first choice. ... At the rate he's declining in the polls, Cain may not even be a factor come the New Year's contests."

The first voting of the GOP presidential primary comes in the Iowa caucus and New Hampshire primary in early January, and Iowa Republican U.S. Rep. Steve King told the AJC that Cain's chances in his state are dwindling.

"There’s been a series of these and by now it surely has to be shutting off or shutting down the fundraising that’s coming to Herman Cain," said King, who strongly defended Cain after the first sexual harassment allegations surfaced. "And whether or not the allegations are true it looks to me like it’s going to be very hard for him to be able to breathe life back into this campaign."

Cain rode his outsider background -- the former Godfather's Pizza CEO never has held elective office -- and his 9-9-9 tax code overhaul to the lead in national polls this fall.

By Monday Cain was declaring he "has nothing to hide" and vowing to answer the latest allegations. Cain’s campaign did not respond to a list of questions from the AJC about White’s claims.

In an email to supporters Tuesday Cain described White as "a friend in need of a supportive hand to better her life. Ms. White has made it apparent that she was abusing the friendship." Cain called the claims "completely false" and asked for "prayers and support."

Several of Cain’s competitors for the GOP nod were asked about the allegations Tuesday but only U.S. Rep. Michele Bachmann, R-Minn., and former Utah Gov. Jon Huntsman were willing to take the issue head-on.

Huntsman told the Boston Globe newspaper that Cain should consider dropping out.

“Every time another accusation comes up, it diminishes our ability to stay focused on the issues that really do matter for the American people,” Huntsman said. “And I think that’s a disservice to the voters.”

In Atlanta on Tuesday, former U.S. Sen. Rick Santorum said the allegations are “troubling.”

Santorum said he and his wife have prayed for Cain – and the other candidates.

Former Georgia congressman Newt Gingrich, whose own extramarital affairs have become media fodder, told CBS News the allegations do not disqualify Cain.

“I think that any candidate has the right to try to recover,” Gingrich said, according to an excerpt released by the network. “They have the right to try to get back in the game. They have the right to try to rebuild momentum.”

Cain donors contacted by the AJC on Tuesday also remained supportive.

"I admire, respect and believe Herman Cain," said Wayne Stoltenberg, a Texas oil executive who has given more than $10,000 in all to Cain's campaign and political action committee, according to federal records.

Arizona state Sen. Lori Klein, who serves as Cain's state chairman, told CBS News she has known him for 12 years and he's "never been anything but a gentlemen -- and I am not an unattractive woman."

Cain spokesman J.D. Gordon the need to reassess the campaign now is similar reassessments at other difficult points.

"My interpretation of that is that we are looking to assess where we are at today and where we need to be moving into the primary," Gordon told the AJC.

The review will include Cain's media appearances and schedule, which has been unorthodox for a presidential hopeful in that he has focused less on key early primary states than other candidates. One apparent adjustment came Tuesday when the Cain campaign canceled a dinner with New York City journalists and politicians scheduled for Sunday, according to the cable network NY1.

Staff writers Jim Galloway and Ariel Hart contributed.