US President Barack Obama's second cousin is running for election as a right-wing firebrand in the state of Kansas.
Milton Wolf's stump speech has involved distancing himself from his relative in the White House and railing against the "Obamacare" health law.
Running under the tea party banner, he aims to oust veteran senator Pat Roberts and become the state's Republican candidate in November's midterm elections.
Mr Wolf, 43, has repeatedly told voters he stands at the opposite end of the ideological spectrum to Mr Obama, who is a Democrat.
He says their blood relationship - Mr Obama's grandmother, Madelyn Dunham, was a cousin of Mr Wolf's mother - is about the only thing they have in common.
Tuesday's primary election is seen as possibly the ultraconservative tea party's last chance to defeat an incumbent Republican senator this election season.
Mr Roberts, 78, is tipped as the favourite to prevail in the intraparty contest.
But the three-term senator has been thrown on the defensive by Mr Wolf's portrayal of him as a typical Washington insider who spends little time in the state he represents.
The Roberts campaign has meanwhile pilloried Mr Wolf, a radiologist, after it emerged he had posted X-ray images of patients' gruesome injuries on Facebook.
A state medical board is reported to be investigating Mr Wolf's uploads, which were accompanied by macabre jokes.
According to the Topeka Capital-Journal, Mr Wolf wrote about one patient with a firearm wound to the skull: "What kind of gun blows someone's head completely off? I gotta get me one of those."
Mr Wolf has apologised for the postings.
Original headline: Obama's Republican Cousin Stands For Election
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