Question: What ethnic group does the incumbent who was challenged by R.J. Harris in the 2010 for the  Republican Party nomination  in the primary election for Oklahoma's 4th congressional district?
Sentence (from "Tom Cole"): As of 2015, Cole – a member of the Chickasaw Nation – is one of only two registered Native Americans in Congress (the other being fellow Oklahoman Markwayne Mullin).
Relevant evidence: Yes