Gov. Henry McMaster speaks during a Republican primary forum at the Greenville County's "Bronze Elephant" dinner Tuesday. The Upstate is expected to play a key role in the outcome of the June 12 GOP primary. Jamie Lovegrove/Staff

GREENVILLE — As the GOP primary for South Carolina approaches the home stretch, all five candidates are counting on a strong performance in the staunchly conservative Upstate, where some of the state's wealthiest political donors and most engaged Republican voters reside.

The contenders have traversed all over the state in recent months, leaving no corner unturned in pursuit of supporters.

But roughly one in three of South Carolina's regular GOP primary voters reside in Greenville, Spartanburg and surrounding counties, according to historical election data.

"The I-85 corridor in the Upstate of South Carolina is one of the most important and Republican-rich areas in South Carolina," Columbia Republican strategist Dave Wilson said. "If you're going to win the nomination, you have to have a strong showing in the Upstate."

Greenville-area voters have already seen a flood of ads and campaign appearances featuring candidates touting their conservative credentials. And they should expect more in the build up to the June 12 contest.

The Greenville County GOP's "Bronze Elephant" fundraising dinner Tuesday night offered another opportunity for the candidates to make their pitches party diehards in the crucial northeast region of the state.

Gov. Henry McMaster has a broad political network in his home base around Columbia. His leading rival, former two-time agency director Catherine Templeton, is a Mount Pleasant attorney with hopes of picking up strong support in the Charleston region.

Lt. Gov. Kevin Bryant is a pharmacist from Anderson, a socially conservative Upstate stronghold that presents a valuable GOP base but remains much smaller than Greenville and Spartanburg. Former Lt. Gov. Yancey McGill, an ex-Democrat, hails from Kingstree in the Pee Dee but like other candidates has focused his time along the Interstate 85/Interstate 26 corridors.

Greenville businessman John Warren jumped into the contest in February, and his mother is active in local GOP politics in the Greenville area. But as a political newcomer who has not run for elected office before, he is still introducing himself to many voters in his hometown. 

That leaves the Upstate ripe for a competitive race.

"Greenville and Spartanburg is going to really be key to any successful statewide campaign," Greenville County GOP chairman Nate Leupp said.

Four of the five candidates attended Tuesday night's forum, which was broadcast live over a popular conservative radio station in the Upstate.

Due to a late night in the state Senate presiding over a debate on a proposal that would ban abortions in the state, a top issue among socially conservative voters, Bryant did not make it.

Buoyed by an expanding business community, Greenville has been one of the fastest growing areas of the state, making economic issues a central factor for many key voting blocs in the area.

While the business community often pushes for lower taxes, the area's rapid population growth has also placed a premium on improving infrastructure that's busting at the seams.

The Upstate's prominent evangelical community puts social issues on the front burner, too. 

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Four candidates have already made the requisite pilgrimage to Bob Jones University, the fundamentalist Christian college that has served as a rite of passage for Republican candidates running statewide in South Carolina.

Pitches required to win over the pro-business and religious wings of the conservative voting bloc may overlap.

"The people who run the corporations are the same ones who go to church," said Dave Woodard, a veteran GOP strategist in the Upstate. "So they're one and the same."

The candidates have left little distance between each other as they have staked out conservative positions on a whole host of key social issues, voicing unanimous opposition to abortion and support for gun rights.

Even though immigration tends to be a more federally focused issue, the candidates have also vowed to crack down on any "sanctuary cities" that arise — jurisdictions that refuse to comply with detainers from immigration authorities.

"Their conservative values are all pretty much the same, so it may just come down to personalities," Leupp said. 

For the first time in a while, Leupp also said voters may take electability into stronger consideration this year as they look ahead to the November general election.

Typically, GOP primary voters have considered the outcome of the general election to be a foregone conclusion. But the early favorite in the Democratic primary, state Rep. James Smith of Columbia, could offer a more viable challenge, Leupp said.

"This election cycle the Democrats look like they may choose someone who is a little less liberal, and if they choose someone with a military background, that might give them a little more play," Leupp said. "So we need to make sure our nominee is able to go head to head with the Democrat nominee."

Follow Jamie Lovegrove on Twitter @jslovegrove.

Jamie Lovegrove is a political reporter covering the South Carolina statehouse and congressional delegation. He previously covered Texas politics in Washington for The Dallas Morning News and in Austin for the Texas Tribune.