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."
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