RALEIGH, N.C. -- On opposite ends of the 1960s-era building that houses the North Carolina General Assembly sit two Republican leaders who have worked hand-in-glove to advance a conservative agenda that had been suppressed by 140 years of Democratic rule of the legislature.

And now those two leaders, North Carolina House Speaker Thom Tillis and state Senate President Pro Tem Phil Berger, are poised to train their fire on each other, as each eyes the Republican Senate nomination and the right to challenge Democratic Sen. Kay Hagan in a state the GOP must win if it hopes to flip the U.S. Senate in 2014. For two Republicans that have collaborated remarkably well, their simmering rivalry is striking in its intensity.

"If these two end up running against each other in a Senate primary it will certainly be an epic showdown," said one North Carolina GOP operative, requesting anonymity to speak candidly. "Some say Berger is interested in running just to run against Tillis."

Hagan is politically vulnerable but strongly positioned at this early stage of her first re-election bid. Recent polling by a North Carolina-based Democratic firm showed the senator's job approval rating slightly underwater at 43 percent, but put her at 49 percent, with an average lead of about 10 percentage points, against eight hypothetical GOP challengers. Hagan raised more than $2 million in the second quarter and reported $4.2 million in the bank.

President Obama's standing, the sluggish pace of economic growth and voters' objections to implementation of Obamacare could weigh on Hagan's midterm prospects. But her political future could ultimately be determined by the outcome of what could be a vicious GOP primary brawl and whether a quality candidate survives a spring nominating contest that could include a runoff.

Tillis and physician Greg Brannon, a libertarian-leaning Tea Party activist, are the only announced candidates. But the political atmospherics of the GOP primary could hinge on whether Berger jumps in. If Berger decides against a run, Charlotte Baptist Pastor Mark Harris, who sources say sees Berger as sufficiently conservative, could join the primary. A Harris candidacy could send the GOP field running right to prove themselves the most conservative on social issues, possibly complicating the party's effort to oust Hagan.

"We're still a Bible-belt conservative state, and social issues still mean a lot to a lot of people. But people remain most concerned with jobs and the economy," North Carolina GOP Chairman Claude Pope said in an interview at the party's Raleigh headquarters.

Tillis and Berger have similarly conservative legislative records, cooperating to push through the General Assembly legislation that would curb abortions, mandate voter identification requirements and reform North Carolina's tax code. Tillis, however, has developed a reputation for putting economic and fiscal matters ahead of social issues that remain key to motivating the Tar Heel State's Republican base. Berger is viewed as more conservative across the board.

A primary pitting North Carolina's House speaker against its Senate president pro tem would be unique -- and could split the state GOP when one considers the entangled alliances Berger and Tillis have built while rising through the ranks. Berger is closely aligned with Rep. Virginia Foxx, who first recruited him to run for state Senate; Tillis shares a consultant with Sen. Richard Burr. Many North Carolina Republicans would find themselves having to choose sides.

Berger and Tillis, during separate interviews with the Washington Examiner in legislative offices just yards apart, offered no hint of a schism that GOP insiders say blew wide open after their common foe, former Democratic Gov. Bev Perdue, retired and Republican Gov. Pat McCrory succeeded her.

But a schism was evident in discussions with their supporters, with one fan of Berger contending that Tillis was insufficiently conservative to win a GOP primary, and a Tillis backer suggesting that Berger wasn't serious about running and would be less formidable against Hagan in the general election.

"I think it's critically important that we have a strong candidate -- solid conservative candidate -- someone that will present a clear contrast with the incumbent," Berger said. "I think I can do that."

Meanwhile, Tillis said that the controversial social-issues bills that he and Berger moved through the General Assembly were "a part of an agenda, but they were not the top priorities given that we came in here on a platform of jobs and the economy, and we had to get that done."