Broun, a physician, has called evolutionary theory "lies from the pit of Hell," and he's sponsoring a drawing to give one of his supporters a free AR-15 semi-automatic rifle. Gingrey, an obstetrician, once defended failed 2012 Missouri Senate candidate Todd Akin's controversial comments about "legitimate rape" and abortion.
It's a free-for-all that highlights the GOP's internal struggle between archconservatives and the business establishment. Some Republicans worry that Democrats could score an upset victory in Georgia's Senate race in November, as they did in a handful of recent Senate and governor's races, if moderate voters find the Republican nominee too extreme.
"It's a microcosm of what we're fighting over nationally," said Kirk Shook, GOP chairman in Oglethorpe County, about 80 miles east of Atlanta. "It's a huge concern for people I talk to around the state, that Georgia could become another Missouri or Indiana. ... I don't want to call any names, but we all know who I'm talking about."
Also in the fray: David Perdue, a businessman and cousin of a former Georgia governor, and former Georgia secretary of state Karen Handel. She narrowly missed out on the governor's office in 2010 before she commanded a national following as a Susan G. Komen Foundation executive during the organization's effort to break with abortion-provider Planned Parenthood.
Most observers expect a May 20 primary to produce a July runoff.
Meanwhile, prohibitive Democratic favorite Michelle Nunn has quietly framed herself as a problem-solver above the rancor she blames for Washington gridlock. Nunn hasn't sought public office before, but she comes with pedigree and connections. Her father, Sam Nunn, represented Georgia in the Senate for 24 years. For years, she has run former President George H.W. Bush's Points of Light Foundation, giving her a claim to bipartisanship and established relationships with wealthy donors.
Democrats believe that's a winning strategy in a state where population growth has closed the partisan gap: President Barack Obama lost Georgia twice, but with little effort he still posted single-digit margins that were much closer than in the rest of the Deep South, where he is intensely unpopular among white majorities. Republicans and Democrats agree that a significant shift of white women to Nunn, particularly in metro Atlanta, would mean a toss-up in November.
The winner will succeed Republican Saxby Chambliss, who is retiring.
Republican consultant Chip Lake, who worked briefly for Gingrey's campaign in 2013, said the key to holding the white suburban vote "is nominating the most electable conservative." Of course, Lake conceded, the GOP primary puts the definition of conservative up for grabs.
"Unfortunately, there's a lot of us in the movement who would rather win that argument than win elections," he said.
All eight Republicans favor repeal of Obama's health care overhaul. All oppose abortion rights. All three congressmen voted against the bipartisan deal to end the partial government shutdown last fall, and Perdue, Handel and the lesser-known candidates all say they'd have voted the same way. So each candidate has tried to carve out distinctions in ways that attract both those who call themselves part of the tea party movement and what Kingston calls "traditional Republicans."
Gingrey's campaign slogan is "Repeal or Go Home," an open effort to take the lead on opposing the health care law. In an interview with The Associated Press, he said that's the top issue for Republican primary voters. Gingrey minimized the internal GOP struggles and insisted that any image of him as extreme comes from Democrats. "I'm an established conservative," he said, "but I'm not a guy with rough edges or the kind of guy who is bombastic even when I'm fighting for Georgia values."
Broun trumpets his absolutism on bellwether conservative issues. He's endorsed by Georgia Right to Life, an anti-abortion group that is more conservative than its national parent because the state outpost wants no rape or incest exceptions in any abortion ban.
In an email inviting his supporters to enter a drawing for the semi-automatic rifle, Broun summoned his overall argument: "We need conservative voices who will not only vote right but will also fight tooth and nail for our values and our rights."
When he announced his campaign, he focused almost exclusively on "out-of-control government spending," and he turns any question about the tea party and establishment back to that issue, calling the national debt "a bipartisan concern."
Kingston, meanwhile, reminds voters that the GOP needs "New England Republicans" to be a national majority party. That, he explains, means accepting Republicans who are more moderate — or at least more quiet — on abortion and gun control but still conservative on tax and regulatory issues.
Kingston regularly reminds voters of his top ratings from leading conservative groups: the National Rifle Association, the American Conservative Union and National Right to Life, among others. He credits the tea party "with the energy that delivered our House majority in 2010." And he touts his role on the House Appropriations Committee in curtailing some federal spending. When he says at one stop that "I've never owned a pistol," he quickly affirms his support for individual gun rights and worries aloud that his comments "can be misunderstood."
Handel and Perdue have largely avoided any philosophical divide by hammering all three congressmen as cogs in the status quo, though Handel in a recent debate slammed "accommodating Republicans" who haven't slashed taxes and regulations enough.
Even amid the maneuvering over style and substance, the two spots in a likely runoff could come down to geography and money.
Gingrey has a sizable campaign account left over from easy House campaigns. He's been a fixture in the Atlanta media market, which reaches much of the state's 10 million residents, for more than a decade. And through redistricting, he's represented a significant portion of metro Atlanta and outlying areas at some point in his tenure.
Kingston is well known across south Georgia, but must introduce himself to the Atlanta area. He should have the money to do that, having raised at least $800,000 each quarter since entering the race to lead all Republicans.
Perdue hasn't held office before, but he's said he's willing to spend enough of his own money to be competitive.
Handel, also from vote-rich north Georgia, trails in the money race but is the only candidate who has won statewide before. And she lost a close Republican primary for governor four years ago despite being outspent.
"Everybody has a path to defeat and a path to victory," Kingston said.
Follow Barrow on Twitter @BillBarrowAP.
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