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Sen. Lindsey Graham, R-S.C., is getting another challenge from the right.

Nancy Mace, the first woman to graduate from the military college The Citadel, will announce her candidacy Saturday in her hometown of Goose Creek, S.C.

Mace, 35, said she would not do interviews until after the event, but confirmed to ABC News today that she intends to enter the race.

Graham, 58, has been hit by criticism from conservatives in South Carolina and nationally who argue that he is too willing to negotiate with Democrats and compromise on some issues.

In an interview on ABC News and Yahoo!'s Top Line in May, FreedomWorks president Matt Kibbe warned Graham not to expect tea party support just because he is an incumbent, calling the sentiment "utterly contrary to Republican philosophy."

"The way he lashed out against [Rep.] Rand Paul, he's begging for a primary," Kibbe told Top Line of the Kentucky Republican Senator.

Kibbe was referring to Graham's criticism of Paul's almost 13-hour filibuster over the Obama administration's drone program.

FreedomWorks said today it's too early to make an endorsement but its activists in South Carolina still have "major concerns with a lot of Graham's votes," specifically mentioning TARP, the Patriot Act and multiple debt-ceiling increases, among others.

"There is an opportunity here for an upgrade, if the right candidate comes along with the united support of the grassroots," FreedomWorks spokeswoman Jackie Bodnar said.

Graham does have money in the bank ($6.3 million), and that's one big reason, despite some conservative discontent, some people in South Carolina still view him as hard to beat.

"Sen. Graham is going to have an incredible financial superiority versus any one he takes on," South Carolina GOP consultant Joel Sawyer said. "That's one thing the other side has to consider. The other part of it is my sense being on the ground here the people unhappy with Sen. Graham are a minority, but a very vocal minority in the Republican Party. It would be a mistake to take those supporters' volume as a wide measure of support. They are very loud, but they are not very widespread."

Sawyer said he isn't sure "how many fired up Lindsey Graham supporters are out there."

"But is there enough discontent to knock off an incumbent? I think that's a pretty tall order," Sawyer said. "For Graham, the danger zone is going into a run-off situation with one challenger. With two or even three challengers, I think that probably helps Graham."

Mace is the former business partner of Will Folks, who runs the conservative South Carolina news website FITSNews. Mace joined the site in 2007 and left in April. Folks says Mace, who's the daughter of a retired brigadier general, neither wrote for the site nor influenced its "editorial policy."

It's an important distinction but an issue her opponents might use against her any way because Folks is best known nationally as the man who claimed in 2010 he'd had an "inappropriate physical relationship" with Republican South Carolina Gov. Nikki Haley three years before. Haley was in the middle of her run for governor when the news broke and denied the claim.

"Nancy Mace is Lindsey Graham's worst nightmare," Folks said in a statement. "She's smart and successful. She's attractive and articulate. She's got a compelling personal narrative, the sort of picture perfect family you see in shopping catalogs and her name fits nicely on a 4X8 road sign.

"Most importantly, she's got ideological convictions South Carolinians can relate to - on spending and personal liberty issues - which will enable her to appeal to a broad swath of voters. None of the other potential challengers to Graham comes close to matching her electability, which is why Graham backers are so afraid of her."

Carolina Conservatives United, a conservative activist group launched by the former co-founder of the Gay Republican group GOProud Bruce Carroll, launched DefeatLindseyGraham.org last week. They are also bringing some heat to Graham, or trying to, with a Web ad that ends with the line, "It's time to bring Lindsey home."

"Everyone is very frustrated because he's not reliably conservative," Carroll said. "We can count on our congressional delegation, we can count on [Sen.] Tim Scott, R-S.C., but we can't count on him and for one of the most conservative states in the nation, that is a source of frustration."

Carroll says they plan to run more Web ads, possibly television ads, and intend to follow him around when he's back on the campaign trail.

"We want to make him answer for some of his votes and comments," Carroll said. "But it's hard to find him back home. He's either in the Middle East or in Washington. We are hoping he visits South Carolina this summer."

Richard Cash, an Anderson County, S.C., businessman, is already in the race, declaring in April.

Cash says he "welcomes" Mace and the "rigorous competition" to the campaign and also had some polite words for Graham, saying he believes he is "sincere and well-meaning."

"But I just profoundly disagree about some very important positions he has taken," Cash, who runs a used automobile business and also an ice cream truck, said.

Cash ran for a U.S. House seat in 2010 and came in a close second to Republican U.S. Rep Jeff Duncan. Cash said he believes that experience will help him even if the primary field gets even more crowded.

"In a field of multiple candidates, my message is powerful enough to set my campaign apart and that's why I'm running," Cash said. "I believe competition is healthy. Nancy or others that get in will force me to be a better candidate. At the end of the day, I'm confident the best choice will emerge to challenge Sen. Graham."

Cash calls Graham "inconsistent," saying "he will be good on one thing and terrible on something else. It's just not clear what his guiding principles are."

Cash, like other conservatives, specifically point to Graham's views on immigration overhaul, Supreme Court nominees and what Cash calls "big government surveillance."

"He stands by his positions and I disagree with them," Cash said.

Graham is not the only high-profile Republican getting primary competition from the right at this stage in the campaign. Kentucky businessman Matt Bevin entered the GOP primary last week against Senate Minority Leader Mitch McConnell. McConnell has been getting some heat from the tea party as well.

"Sen. McConnell, conservatives don't need a chicken when it comes to Obamacare," warned an internet ad released this week from the group For America. "Leaders lead. But if you fund it, you own it."

State Sen. Lee Bright has also said he might get into the race against Graham. The primary candidates will face off against each other in June. The other U.S. Senator from South Carolina, Tim Scott, is also up for re-election in 2014. He was appointed to his seat last year when Jim DeMint resigned. Scott has no primary challengers at the moment.

Graham's campaign said it will "weigh in after a formal announcement" from Mace.