CHARLESTON, South Carolina (CNN) -- After a two week political free-fall, Sen. John McCain received welcome news late this week when a new CNN poll showed he still maintained strong Republican support in South Carolina, a crucial Southern state with an early primary.
Sen. John McCain had disappointing campaign fundraising during the second quarter.
The senator from Arizona was standing firm despite an implosion that has temporarily crippled his presidential campaign.
But if the one-time frontrunner hopes to re-energize his presidential bid, he is going to have to convince the likes of Cyndi Mosteller that he is the only candidate who can keep the White House in Republican hands.
Mosteller, a former chairwoman of the Charleston County Republican Party, is a true grassroots activist who is willing to speak her mind and defend her candidate from attacks and criticism by opponents.
She was a vocal advocate for McCain in South Carolina during the 2000 presidential contest when supporters of then-Texas Gov. George Bush effectively derailed his bid to win the South Carolina primary.
This time, with McCain now appearing at his weakest, McCain won't have Mosteller to defend him. She is waiting for former Sen. Fred Thompson of Tennessee to formally enter the race.
"My intentions are at this point, when he becomes a candidate, I am going to support him," Mosteller said in an interview Friday in her office, which is just steps away from a sweeping view of the Ravenel Bridge.
The former county chairwoman said she holds no animosity toward McCain, and still describes him in glowing terms.
"He is one of the most honest and strong Americans on the floor of the U.S. Senate," Mosteller said.
It was not the recent revelations of financial mismanagement in the McCain campaign or his successful push for campaign finance reform -- opposed by many of her like-minded social conservatives -- that caused her to part ways with him.
Mosteller said her decision to back one of McCain's potential rivals came down to his support for immigration reform.
"I see it as a national security issue," she said. And Mosteller predicted that other McCain backers who oppose his stand on immigration also will turn away from McCain to support Thompson.
Two weeks ago, Mosteller said she co-hosted a meeting at a downtown Charleston hotel for more than 30 Republicans interested in backing Thompson.
The group consisted of people already backing McCain and several of the social conservative candidates in the race such as Kansas Sen. Sam Brownback, former Arkansas Gov. Mike Huckabee and California Rep. Duncan Hunter.
"He [Thompson] sweeps up a lot of support of the second tier candidates," she said, and added, "People who disagree with McCain on immigration will go to Thompson."
While McCain has been under fire for months from conservatives for his stand on immigration, Mosteller said it was not until the legislation started moving toward the Senate floor did she understand the details of what critics described as "amnesty" for illegal aliens already living in the United States.
"I think John McCain thought it would be seen by the American people as a strong American bill," she said. "But I think many people came to feel it was an abandonment of America's first principle to protect itself."
Thompson's own conservative credentials have come under scrutiny since billing records revealed he consulted a pro-abortion rights group during his time as a lobbyist in the early 1990s.
A Thompson spokesman told CNN last week that Thompson "has no recollection of doing work on behalf of this group."
The spokesman added: "It is not unusual for a lawyer, when asked by a colleague, to provide counsel or assistance when asked, including on matters on which they personally disagree."
For Mosteller, who is a vocal anti-abortion rights advocate, Thompson's previous work for the pro-abortion rights group is not enough to disqualify him as an appealing candidate to social conservatives. She pointed to his solid anti-abortion rights voting record in the Senate as evidence of his socially conservative beliefs.
"He was taking a case," she said. "In that scenario, Fred Thompson was advocating for a client, not a cause."
Even though she is no longer backing McCain, Mosteller noted that in the very least he deserves respect from South Carolinians for standing by President Bush on two unpopular issues -- the Iraq war and immigration --- even though she personally disagrees with him on the latter.
"John McCain has been maligned for not being supportive of the president," she said, alluding to the lingering resentment of McCain by Bush supporters following the bitter 2000 presidential primary.
"He should be given credit for standing with the president and going to the wall on the issues of Iraq and immigration," she said.
As Mosteller was breaking away from McCain, the GOP senator's campaign was working to reassure supporters that he remains focused on the presidential race.
In an internal strategy memo, the McCain campaign described South Carolina as their "best organized state, and one that will reward his steadfast position on Iraq."
His campaign also claimed that his chief rivals for the GOP nomination all have their own problems in the state.
McCain placed a respectable second place -- behind Rudy Giuliani -- in CNN's latest poll on South Carolina, conducted by Opinion Research Corporation. However, the survey it also contained troubling news for the senator. Thirty-four percent of Republican primary voters said they would not support McCain "under any circumstances" in his bid for the White House.
Would a change of heart on immigration help McCain with South Carolina voters such as Mosteller? Perhaps, but the one-time McCain supporter predicts it will never happen.
"I think John McCain will not change because ... he is so principled," she said, with a hint of admiration in her tone. E-mail to a friend