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The chairman of the Mississippi Republican Party said Thursday that the state senator challenging Republican Sen. Thad Cochran should explain why he was listed as a keynote speaker at an event that included a group that sells "white pride" merchandise.

State Sen. Chris McDaniel, who is challenging Cochran, had been listed as a speaker at the Combined Firearm Freedom Day/Tea Party Music Fest in Guntown, Miss., on May 17. Listed as a vendor at the rally is Pace Confederate Depot, a group that "deals in Confederate, Tea Party, and White Pride Merchandise," according to its website.

McDaniel spokesman Noel Fritsch said Thursday that McDaniel would not attend. "Chris McDaniel never agreed to attend the event and will not attend the event," he said.

Mississippi GOP chairman Joe Nosef told NBC News Thursday that McDaniel should clarify whether he supported the group.

"I think he should clear it up as fast as he can," Nosef said. "Running for the United States Senate is a very important thing and as a party we need to always be careful and focused and serious about what our views are and what our interests are. And if Sen. McDaniel thinks that there's more to tell, to explain it, my thought as the party chairman would be, the sooner the better."

Mississippi Senator Chris McDaniel speaks during a town hall meeting in Ocean Springs, Miss., March 18.JONATHAN BACHMAN / Reuters file

The back-and-forth is the latest skirmish in a broader fight between establishment Republicans and conservative and tea party groups. The Mississippi race is viewed as conservative organizations' best chance to oust a sitting GOP senator in the 2014 midterm elections. The Club for Growth, FreedomWorks, and other national conservative groups have endorsed McDaniel; the National Republican Senatorial Committee in Washington is supporting Cochran, the incumbent.

National establishment Republicans are concerned that insurgent conservative candidates could cost the party critical seats -- and possibly overall control -- of the Senate this year. So far, the phenomenon has cost them as many as four Senate seats already; conservative candidates in Indiana, Colorado, Missouri and Nevada all beat more moderate GOP candidates in primaries only to go on to lose the general election to a Democrat.

Establishment groups like the NRSC are determined to avoid that this election cycle, when the GOP needs to win 6 seats to take back the Senate. Highlighting potential trouble spots early on is one way to advance that goal. The NRSC has also focused on Matt Bevin, who's running in Kentucky against Senate Minority Leader Mitch McConnell; Bevin recently appeared at a rally to legalize cockfighting.

"I want the strongest Republican candidate nominee in order to win the election in November," said Nosef, the Mississippi GOP chair. "And if there is any information that some voter might find negative, certainly I hope we deal with all of that in our primary and not when it's too late."

Pace Confederate Depot is just one of many groups listed as attendees at the event, billed as a "Battle for the Constitution"; also included are tea party and liberty groups. A new version of the graphic advertising the event does not include McDaniel's name as a speaker.

The Southern Poverty Law Center lists Pace Confederate Depot as an "active white nationalist group," and owner Brian Pace told a Mississippi TV station last year that "whenever we had racial segregation, things were much better off."

Asked if white nationalist rhetoric had a place in the state's Republican Party, Nosef said: "No. Absolutely not."