In a letter to McDaniel's attorney, the state's GOP chairman, Joe Nosef, said it wasn't possible for the party's committee of 52 volunteers to pore over his voluminous challenge in a prudent manner.
"Given the extraordinary relief requested of overturning a United States Senate primary in which over 360,000 Mississippians cast votes, the only way to ensure the integrity of the election process and provide a prudent review of this matter is in a court of law," Nosef wrote.
McDaniel, a state senator and tea party favorite, lost to Cochran by about 7,600 votes on June 24. Three weeks earlier, he had edged out the six-term senator in the primary but failed to reach the 50% threshold needed to clinch the nomination.
Cochran boosted voter turnout in the runoff by appealing directly to Democrats and African Americans. Under Mississippi law, anyone who did not vote in another party's primary was eligible to cast a ballot in the Republican runoff.
McDaniel filed his challenge Monday with 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 take his grievance to court.
In a news conference Monday, McDaniel called on the party to review the runoff results and declare him the victor, calling his challenge "a chance for our party to take the lead" in integrity.
McDaniel's attorney, Mitchell Tyner Sr., contended 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. An additional 9,500 ballots had irregularities, he said.
Nosef noted in his letter that seven days' notice is required before the executive committee can meet, according to state law. If the notice were sent Wednesday, the earliest the committee could gather was Aug. 13 -- one day before the legal deadline for McDaniel to go to court.
"It is neither prudent nor possible in a single day for any political committee to process and review the significant amount of complex evidence necessary to make such a decision, and attempting to do so would be prejudicial to both candidates," Nosef said in a statement separate from the letter.
Tyner said in a statement that his client was "very disappointed" the committee would not hear his challenge, according to the Associated Press.
Despite the bitter intraparty feuding, Republicans remain overwhelmingly favored to retain the seat in conservative Mississippi. But they could have a fight ahead against Democratic candidate Travis Childers.
McDaniel was once seen as the tea party's best hope this midterm election cycle to topple an establishment GOP senator seen as insufficiently conservative. But after he lost the runoff, national conservative groups moved on to other battles -- including Tennessee, where Republican Sen. Lamar Alexander faces off against tea party challenger Joe Carr on Thursday.
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Times staff writer Lisa Mascaro contributed to this report.