It's not easy to get to the right of U.S. Rep. James Lankford, a staunch conservative from a state that prides itself on being "the reddest of the red." The Baptist minister and onetime leader of one of the nation's largest Christian youth camps came to Congress three years ago and has preached a hard-right doctrine heavy on gun rights, abortions and the evils of Obamacare.
Yet Lankford, a rising star in the national GOP, now finds himself fighting for political survival in a primary election for a U.S. Senate seat that may show whether the insurgent shock wave that felled leading Republican Eric Cantor in Virginia extends into this part of the nation's Republican heartland.
Lankford, 46, is being challenged by another conservative, T.W. Shannon, the former speaker of the Oklahoma House of Representatives. The race, which focuses on Lankford's role in GOP leadership positions, has drawn advertising money from national conservative organizations and has left even tea party groups confused over who to support.
National tea party organizations are weighing in for Shannon, but local groups, some of which have backed Lankford in previous races, haven't chosen sides.
"They all go to church, probably donate to charities and help little old ladies cross the street," said Mark Keeling, a truck driver who heads up the local tea party chapter in Chickasha, a semi-rural town of 16,000. "The problem is, you don't really know who these guys are."
Drawing further attention to the race is the challenger's ethnicity: Shannon, 36, was the state's first black speaker of the House and is also Native American, a valuable asset for a party struggling to diversify outside its overwhelmingly white voting bloc.
The election might shed light on whether a tea-party favorite risks his grass-roots credibility if he moves up in the GOP he's pledged to reform. Five other less-funded Republicans will also be on the ballot next week, along with three Democrats, vying to replace retiring Republican Sen. Tom Coburn.
Lankford was a political unknown when he won an open seat in Congress in 2010 from Oklahoma's Republican-leaning capital city.
Thin, with red hair and a preacher's booming voice, he leveraged an army of young evangelicals from his Baptist network to propel his campaign, and he's now counting on them again in a statewide race.
Lankford has been campaigning as he legislates — like a workhorse. The congressman happily delves deep into nuance with voters who ask about complicated federal budget issues or congressional investigations.
But Shannon, a striking presence at 6-foot-4 and impeccably dressed, describes himself as the more conservative and aims to exploit the sliver of room to the right of Lankford, who became House Republican Policy Committee chairman because of his grasp of GOP issues. For some conservatives, that raises the specter of a Washington insider.
"I get that," Lankford said recently. "That's just the dynamic of it."
A particular target of pro-Shannon ads is Lankford's votes to increase the nation's debt limit and to support a bipartisan budget agreement.
"Mr. Lankford: The truth is, these are not our Oklahoma conservative values," says one ad funded by an independent group.
Lankford defended those votes as the result of hard-fought battles with a Democratic Senate and president.
"The issues I'm being attacked on are issues that say, basically, you should close the government," Lankford said.
Shannon, a protege of J.C. Watts, who in the 1990s became the first black Republican congressman from the South since Reconstruction, climbed the leadership ladder in the state legislature by cultivating the party's right wing. As speaker, he created a special committee to hear proposals for defying the federal government.
Shannon, whose father, a school teacher, is black and a Chickasaw and whose mother is African-American, says there should be nothing unusual about a black or Native American conservative.
"I think we're beyond the days where that's a major issue in the race," Shannon said before a candidate forum.
But it's unlikely Shannon will get much support from those traditionally Democratic groups, even in his hometown of Lawton, a rough-and-tumble Army post town.
"The Republican Party has thrown us off the bus, and I'll be doggone if I'm going to vote for a black dude that drives the bus over me," said Jim Floyd, 84, a retired African-American Army officer and Democrat who has lived in Lawton for 50 years.
Shannon's membership in the Chickasaw Nation has been a fundraising asset. The tribe operates the state's largest casino and leaders of several Oklahoma-based tribes are backing him financially.
The fierce attack ads from both sides have drawn a rebuke from Coburn, the hugely popular conservative maverick, who decried politics "in its very worst form with misleading advertisements and allegations against candidates."