Sen. John McCain (Ariz.), former Massachusetts Gov. Mitt Romney and the other Republican presidential frontrunners aren’t the only ones with a lot riding on South Carolina’s GOP primary Saturday. Lindsey Graham and Jim DeMint, the Palmetto State’s popular conservative Senators, hold tickets for competing horses in the GOP stakes race.

And on primary day, the political operations of both first-term Senators will be on center stage.

Graham, who has supported McCain’s presidential ambitions since the Arizonan’s dramatic defeat at the hands of then-Texas Gov. George Bush (R) in 2000, has taken the lead in McCain’s effort to make inroads with the state’s GOP establishment.

Meanwhile, DeMint has turned over much of his political team to Romney.

Eight years ago, Bush won South Carolina with more than 53 percent of the vote by mining the state’s network of Republican lawmakers, fundraisers and military personnel. McCain, using Graham’s contacts in the state, is banking on the same model to turn out the vote on Saturday.

“Both Sen. Graham and Sen. DeMint have won statewide in South Carolina, so they understand various areas of the state and who the political players are in the state,” a state Republican source said. “[But] Sen. Graham has really helped Sen. McCain lock up some of the [Republican] establishment support in South Carolina, support that went against him in 2000.”

McCain, a former Naval officer, spoke at the Citadel’s 2002 commencement and attended the funeral of a prominent Republican state lawmaker at Bob Jones University in late 2000, drawing praise from prominent Greenville-based state Sen. Mike Fair (R) and other high-profile conservatives in the state.

Shepherded by Graham, McCain also has spent the past eight years raising money and campaigning for local GOP candidates, lending his likeness to their direct-mail pieces and handing over more than $180,000 out of his political action committee, Straight Talk America, to local party committees and state Assembly candidates.

Graham and McCain successfully enlisted Bush’s 2000 fundraising team, and two of Graham’s top political hands, Richard Quinn and Trey Walker, were brought on board by McCain’s presidential campaign.

But in South Carolina, a state that feeds on Republican politics, there always are plenty of endorsements — and hired guns — to go around.

Facing McCain’s six-year head start, a DeMint staffer said Romney’s initial strategy in the state included bringing in DeMint and leaning on the organizational remains of his 2004 Senate run. DeMint endorsed Romney in late 2006.

“Our entire grass-roots organization turned over for the governor,” the staffer said. “There are 46 counties in South Carolina, and Gov. Romney has chairmen in 46 counties.”

“If you compare them to state Republican Party county chairmen list, they’re almost identical,” the staffer added. “Everyone that’s county chairman for the Republican Party is basically a county chairman for Romney.”

The staffer also downplayed McCain’s support among state lawmakers, arguing that activists will turn out the vote on primary day and that the recent furor over McCain’s and Graham’s vocal calls to overhaul the country’s immigration laws has soured the Republican base on both men.

“From a grass-roots standpoint, state House Members and state Senators are close to their voters, but they’re really not going to help you that much when you’re running a statewide presidential campaign,” the DeMint aide said. “We’ve got all of the guys that helped get these Members in their House and Senate seats, turn over to our guy [Romney] to get him elected.”

McCain political strategist Walker’s response?

“That’s usually what campaigns say when they don’t have the establishment behind them,” he said. “I’ve used that line before.”

DeMint’s political team also has migrated over to Romney’s team. Warren Tompkins, who has worked on campaigns for DeMint and Graham, and Terry Sullivan, DeMint’s former campaign manager, now both work for Romney.

“It’s a small universe here,” a state Republican source said. “There are people on the Romney team that the Graham people are very familiar with. Some of them helped [Graham] on his 2002 campaign.”

Katon Dawson, chairman of the South Carolina Republican Party, called the involvement of both Senators rare in a presidential campaign. DeMint’s and Graham’s predecessors, former Sens. Fritz Hollings (D) and Strom Thurmond (R), rarely dabbled in presidential politics during their last two decades, Dawson said. But he hinted that DeMint and Graham’s involvement amounted to much more than a political sideshow — a suggestion echoed by other lawmakers from the state.

“The fact that they’re both out front makes it extremely competitive between the two,” Dawson said. “Certainly, they trust their judgment on legislation and a lot of issues … [but] in South Carolina, endorsements don’t transfer into direct electability — it leads to [the state’s] independent streak.”

Rep. Bob Inglis (R-S.C.), who is backing former Arkansas Gov. Mike Huckabee (R), said that while endorsements are not without merit, their impact on the race should not be overemphasized.

“I don’t think that support is transferable,” Inglis said. “I’m not sure that organization is transferable either.”

Inglis said voters will make their decisions based on many factors and that ultimately the contest will be decided on the principals themselves, not their surrogates.

“It’s going to be about the strength of McCain versus the strength of Romney,” he said.

Rep. Joe Wilson (R-S.C.), who is neutral in the presidential race, said the involvement of Graham and DeMint is a positive for both the McCain and Romney campaigns.

“Both U.S. Senators will have a great impact,” he said.

Wilson also noted that while Republican presidential primaries have historically been very divisive in the state, they also produce some positive results for the state’s Republican Party.

Because voters in the state do not register by party, presidential primaries are a good way to identify new voters who lean Republican and to update and build the GOP’s voter file, Wilson said. He said in the end, all of the Republicans in the state benefit.

Wilson also said that he has been on both the winning and losing sides of presidential contests in the state. This time around he chose not to endorse a candidate — not because he couldn’t find one whom he likes, but because there are multiple candidates whom he finds appealing.