By Heide Brandes and Jon Herskovitz
(Reuters) - In staunchly conservative Oklahoma, three major candidates are running in Tuesday's Republican primary for a U.S. Senate seat, two have a shot at winning and one is gathering attention because he is half black and half Native American.
T.W. Shannon, 36 and the youngest speaker of the House in Oklahoma, is a member of the Chickasaw Nation and represents a bit of diversity that has captured the attention of the national Republican Party looking to expand its base of white voters.
But polls show U.S. Rep James Lankford, 46 and a former leader of a massive Christian youth camp, slightly ahead of Shannon in the race that has exposed rifts within the tea party branch of the Republican Party.
Tea party darling Ted Cruz, a Republican U.S. senator from Texas, has endorsed Shannon, calling him a "conservative fighter, while an Oklahoma tea party group has rejected Shannon, saying in an open letter he has "too many masters to serve", including Native American tribes.
Both candidates have been running as hard-right conservatives who will defeat the Obama administration's agenda.
If neither gets a majority, the two head to a runoff in August, with the winner emerging as the favorite for the Senate seat due to the Republican dominance in the state.
More so than in other states, Native Americans have ingrained themselves into Oklahoma's social fabric, making up about 9 percent of the state's population.
This has created some backlash from ranchers who feel land grants to tribes have been exorbitant. Social conservatives dislike the casinos on Native American lands, seeing contributions from the tribes to Shannon's campaign as tainted.
Shannon has said his roots have helped him bring unity.
"Chickasaw values are Oklahoma values," he said in a recent TV appearance.
Outgoing Senator Tom Coburn, a Republican who is retiring, has been seen as keeping the playing field level, criticizing aspects of both campaign he sees as unjust.
One reason Lankford has the edge is that he comes from a larger constituency and is seen as better with national issues due to his time in the U.S. House, said Oklahoma States University political science professor Brandon Lenoir.
"The fact that Shannon is Native American and African American will be an appealing factor for a sector of the population, but traditionally, African Americans and Native Americans do not vote Republican," said Lenoir.
(Writing by Jon Herskovitz; Editing by Nick Zieminski)