McDaniel, the tea party favorite, lost the race by more than 7,000 votes to Sen. Thad Cochran, after the GOP incumbent engaged in a controversial strategy to recruit Democratic and African-American voters to the polls.
A prolonged and bitter fight is a scenario GOP leaders in Mississippi and Washington have tried to avoid as Democrats increasingly eye the Magnolia State as a fractured battleground where they could make gains in the November election.
Republicans remain overwhelmingly favored to retain the seat in conservative Mississippi, but they could have a fight ahead against Democrat candidate Travis Childers.
At a news conference in Jackson, McDaniel called his challenge a "chance for our party to take the lead" on honesty and transparency in government.
"Mistakes were made," said the tea party candidate, a state senator. "That's what we're here for today. That's why this challenge is so important."
Already, the race that wrapped up June 24 has been one of the oddest this year, with a criminal investigation into allegations that McDaniel allies took a photo of Cochran's ailing wife in her nursing home. Later, tea party campaign workers apparently got locked inside a polling station on election night. One McDaniel backer implicated in the photo incident committed suicide.
McDaniel was once seen as the tea party movement's best hope this midterm election cycle to topple an establishment GOP senator seen as insufficiently conservative. But after he lost the primary runoff to Cochran in a contest with racial overtones, national conservative groups have moved on to other battles.
McDaniel, though, just kept going and his team has repeatedly fought to open the election books to scour the results.
McDaniel's attorney Mitchell Tyner Sr. said Monday that as many as 3,500 votes were cast in violation of state rules -- presumably Democrats who voted for their own candidate in the primary, then crossed over to vote for a Republican in the runoff. Another 9,500 ballots, he said, had irregularities.
In Mississippi, where the state government plays only a minor role in overseeing the election process, the results for the primaries are certified by the state parties.
In this case, McDaniel is challenging the executive committee of the Mississippi Republican Party, which under state law has 10 days to decide whether to hear the case. After that, McDaniel can bring his grievance to the courts.
Cochran’s attorney Mark Garriga said the McDaniel campaign has made “repeated and baseless allegations of fraud and misconduct.”
“We look forward to holding the McDaniel campaign to the burden of proof that the law requires -- and, we are dedicated to the defense of the votes of those Mississippians who voted on June 24 for Thad Cochran as their United States Senator,” Garriga said.
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