Both the U.S. Chamber of Commerce and Karl Rove's American Crossroads have thrown their support and dollars behind Thom Tillis, speaker of the state House, as party elders try to secure their favored candidate to confront first-term Democratic Sen. Kay Hagan in November.
But it's Greg Brannon, a conservative, Christian ob-gyn -- who was born in Inglewood, Calif., and graduated from USC -- who has captured the passion of the tea party-aligned wing of the GOP. Brannon's allies say Tillis is not conservative enough for Washington.
On Monday, surrogates swooped into North Carolina from the highest rungs of the party's divided ladder for the slugfest. Tea party hero Sen. Rand Paul (R-Ky.) stumped in the Tar Heel State for Brannon, while former GOP presidential nominee Mitt Romney announced his support for Tillis.
Like elsewhere in the Senate races, the hard-line GOP candidates are being brushed back by an onslaught of support from the establishment. Party leaders are trying to avoid nominating extreme candidates that could dash GOP hopes of gaining the six seats they need to retake control of the Senate in midterm elections this fall.
A similar battle has already been won in Texas, where Sen. John Cornyn, the No. 2 Republican in the Senate, trounced his primary challenger in March. In June, Republican Sen. Lindsey Graham appears well-positioned to swat back a cast of challengers in South Carolina.
The next big skirmish happens later this month when Republican Sen. Thad Cochran of Mississippi and Republican Sen. Mitch McConnell of Kentucky, the Senate minority leader, take on their tea-party-aligned challengers.
Hagan is among the most vulnerable Democrats up for reelection this fall, and her campaign is increasingly worried about a Tillis victory, as polls show him leading Brannon.
Hagan's camp took the unusual step of recently running a radio ad apparently intended to help Brannon, whom experts say would be easier for her to beat in the general election. The ad tears into Tillis' support for certain aspects of Obamacare, portraying him as soft on a signature GOP issue.
Hagan, who supported Obamacare, defended the ad, accusing Tillis of waffling on the healthcare law.
Tillis has promised to repeal Obamacare.
The Hagan campaign dashed off a memo on the eve of Tuesday's primary vote, detailing the ways it would attack Tillis in the general election. The memo, obtained by the Los Angeles Times, says the strategy will focus on Tillis' record in the statehouse passing North Carolina's restrictive new voting laws and refusing to expand Medicaid under Obamacare.
On the Democratic side, Hagan needs to clear her primary too.
But the main Democratic race to watch is that of former "American Idol" star Clay Aiken, who is trying to win the party nod for the chance to challenge Republican Rep. Renee Ellmers for a House seat.
Even if Aiken pulls out a primary victory, that suburban seat outside of Raleigh remains all but out of reach for Democrats, thanks to the last round of redistricting that carved up more Republican seats in the House.
All of the primary candidates need to clear 40% to avoid a runoff.