RALEIGH, N.C. — First dubbed the "Research Triangle" back in the 1950s, the iconic nickname for central North Carolina's politically fluid Piedmont region is an apt moniker for Republicans' effort to oust Democratic Sen. Kay Hagan in 2014. The work the GOP does here will have implications well beyond the Tar Heel State.

Can the eventual Republican nominee, in all likelihood a conservative white male, defeat a female incumbent with a moderate image in a state where the key to victory lies with white suburban women swing voters? Will North Carolinians respond favorably to a Republican who will be defined at least in partially by divisive social issues? Can Republicans make President Obama and his unpopular health care law a winning issue?

Republican prospects for winning control of the Senate improved markedly this month when former Montana Gov. Brian Schweitzer, a Democrat, decided not to run for his state's open seat. But flipping the six seats it needs to take control of the chamber, the GOP will have to stretch a competitive Senate map beyond the solid red states, and their performance against Hagan in purple North Carolina could be indicative of just how successful — or not — the 2014 mid-terms are for the GOP.

"By all accounts, there is no path to having a Republican majority leader that doesn't lead through North Carolina," Thom Tillis, the state House speaker and leading Republican Senate candidate, said in an interview in his legislative office. "This is the quintessential swing state."

Electoral results since 2008 tell the story. That year, President Obama won North Carolina by fewer than 14,000 votes and Hagan outperformed him, defeating incumbent GOP Sen. Elizabeth Dole by 8.5 percentage points. Four years later, while Mitt Romney struggled to pull out a 2.2 percentage point victory over Obama, now-Gov. Pat McCrory, a Republican, was cruising on his way to an 11.5-point landslide over Democratic Lt. Gov. Walter Dalton.

In between, Republicans rode a Tea Party wave and steamrolled the Democrats in 2010, ending 140 years of Democratic rule of the state legislature while re-electing GOP Sen. Richard Burr and flipping three formerly Democratic congressional seats.

Meanwhile, North Carolinian are increasingly moving away from the two major parties. Since 2008, the number of Democratic voters dropped by nearly 3 percentage points, and they now account for about 43 percent of the state's voters while the Republican Party dropped about 1 percentage point to 26 percent of the electorate. The number of voters identifying themselves as independents, however, rose by nearly 4 percentage points and now account for more than a quarter — 25.9 percent — of the vote.

It's this growing bloc of "unaffiliated" voters, particularly white, suburban living in battleground counties, that could sway the 2014 Senate race. To take the Senate seat, a candidate would likely have to win a majority of the 2012 Obama-McCrory voters and about two-thirds of the independent, or unaffiliated, voters who view themselves as ticket splitters. Having labored in office to project a pragmatic focus on North Carolina issues, Democrats view Hagan as better positioned on this front.

"Her strong record of bipartisanship and results-focused leadership is what will resonate with voters during this campaign," Hagan campaign manager Preston Elliott said.

Democrats believe the Republican-controlled legislature's push to curb abortions and require voters to show identification at the polls will boost Hagan by mobilizing women and African American voters. The claim is straight out of the national Democratic playbook and would probably be overblown if not for the fact that the Republican candidate could be top legislative Republicans: Tillis or state Senate President Pro Tem Phil Berger, who has not yet joined the race.

Tillis and Berger have worked hand-in-hand on a host of legislation, including bills focused on balancing North Carolina's budget, economic growth and tax reform, and Republicans concede that that may focus the race on state issues rather than federal matters. But the GOP also insists that even if state issues come into play, either Tillis or Berger would remain strong contenders against Hagan.

Republicans offer that Hagan has built her political foundation on a strong constituent-services operation — a move they say pays homage to the late GOP Sen. Jesse Helms, who was practically untouchable here when North Carolina was a reliably Democratic state. Still, they believe she is vulnerable, citing continued anxiety over the national economy, a Senate voting record that is far more liberal than centrist, and her support for Obamacare.

Hagan has been a dependable vote for Obama and Democratic Senate leadership. But the one vote that may prove most problematic is likely to be her unwavering support for Obama's signature health care reforms. With Obamacare set to begin next year, opposition to it in North Carolina has grown palpable, Republicans said.

"While she's a formidable candidate," Berger said, "I think that's a race that's clearly winnable and it's a race that I think is something that should be looked forward to."