Mark Clayton, 35, received more than twice as many votes as the runner-up in Thursday's primary, The (Nashville) Tennessean reported. Party officials said that's because his was the first name on the ballot in a long list of little-known challengers.
In a news release, the party said Clayton votes in Democratic primaries only when he is running.
"Mark Clayton is associated with a known hate group in Washington, D.C., and the Tennessee Democratic Party disavows his candidacy, will not do anything to promote or support him in any way, and urges Democrats to write-in a candidate of their choice in November," the party said.
Tennessee was once a Democratic stronghold, represented by such well-known senators as Cordell Hull, who later served as President Franklin Roosevelt's secretary of state, Estes Kefauver, Al Gore Sr. and Al Gore Jr., who served two terms as U.S. vice president.
The state has turned Republican and the freshman incumbent, Bob Corker, is believed to be unbeatable, The Tennessean said.
Clayton is involved with Public Advocate for America, a group that opposes abortion and gay marriage. He said Tennessee Democrats are engaging in "zero-sum politics."