South Carolina’s Republican presidential primary could lose its national luster if Gov. Mark Sanford decides to run for the White House in 2008.

Other GOP contenders, knowing they would have no chance in a candidate’s home state, simply would bypass South Carolina and take their campaigns — and millions of dollars — elsewhere.

“It would devalue the primary,” says Robert Botsch, a political science professor at USC Aiken who does not participate in partisan efforts. “There’s little to be gained by challenging a favorite-son candidate.”

Worse, he adds, “It would take us out of the national spotlight.”

South Carolina’s first-in-the-South primary has emerged in recent years as one of the nation’s most important presidential contests.

Often, it has combined with Iowa and New Hampshire to define — and even settle — the battle for the GOP nomination.

In 25 years, no candidate has won the GOP presidential nod without first winning the South Carolina primary.

Sanford has done nothing to quiet months of speculation that he might run for president.

“It’s too early to be talking about 2008,” he says.

South Carolina landed the South’s leadoff primary for the 1980 election when then-state GOP chairman Dan Ross, the late GOP consultant Lee Atwater and other state Republicans engineered the move to give a head start to Ronald Reagan. The move produced lots of national attention for the state.

State Republicans have jealously guarded that spot since.

Today, the South Carolina contest remains a pivotal, perhaps decisive, showdown.

With no incumbent running, the 2008 contest is likely to attract a large field.

Two potential candidates, Massachusetts Gov. Mitt Romney and former New York Mayor Rudy Giuliani, visited the state this month. More are expected.

Most South Carolinians aren’t paying attention to the candidates, but political activists are. And the courting of these activists — whose tireless, on-the-ground efforts can turn an election — is extensive.

National reporters and candidates won’t move into the state for a while yet. It’s early.

But once that day arrives, the state will be crawling with media types, political consultants, candidates, TV talk show hosts, and thousands of campaign volunteers bused in from all over.

Restaurants and bars will be jam-packed. Hotels will be filled to capacity. And parking garages will be full.

There will be a level of excitement that only political campaigns can bring.

That is, if Sanford doesn’t run.

His candidacy “would have the potential of making the South Carolina primary insignificant,” says College of Charleston analyst Bill Moore, who does not participate in partisan efforts.

“Bottom line: A Mark Sanford candidacy would diminish the importance of this primary.”

Francis Marion University professor Neal Thigpen, a GOP activist, says a Sanford candidacy “would take something away from the state Republican Party which has been instrumental in building the party and putting this state on the national map.”

“It would deny rank-and-file voters the opportunity to express a preference among the leading contenders... and that would not be good.”

The state GOP is preparing for 2008 as if Sanford won’t run. It is taking steps to protect its first-in-the-South status.

“We have put everyone on notice that we will be the first,” says state GOP chairman Katon Dawson.

In the end, the state gains economically from hosting the high-profile primary. In 2000, roughly $20 million was spent by the two campaigns here, Dawson says. That doesn’t count another $4 million the national media would bring.

Certainly, many Republicans are privately saying, Sanford wouldn’t want the state to lose that money.

The message?

Don’t run, Mark.