Washington (CNN) -- Chris McDaniel on Monday officially contested results showing he lost a Republican primary to Mississippi Sen. Thad Cochran, revealing what his camp alleges is evidence of voter fraud and other irregularities.
"They asked us to put up or shut up. Here we are. Here we are with the evidence," McDaniel said at a news conference in Jackson.
McDaniel, a state senator, has refused to concede the June 24 runoff result and filed a formal challenge with the Mississippi Republican Party's executive committee. The case could eventually wind up in court.
The challenge outlined claims of more than 15,000 cases of illegal or questionable votes, of which 3,500 were crossover votes. The official state count puts Cochran ahead by more than 7,600 votes.
McDaniel is asking to make the case publicly before the state GOP executive committee and he anticipates a "hearing in a public forum."
Cochran's campaign said it had retained a lawyer to fight the allegations, which it dismissed out of hand.
The election speaks to a struggle within the GOP between establishment figures, like Cochran, whose been in the Senate for more than 35 years, and McDaniel, who represents a new breed of arch conservatives backed by the tea party.
Allegations included in more than 250 pages of affidavits claiming that 3,500 voters cast ballots for a Democrat in the first leg of the primary before crossing over in the Republican runoff election. If true, those votes cannot be counted in the runoff.
McDaniel's lawyer, Mitch Tyner, called another 11,000 more votes questionable or "improperly cast."
Many affidavits were signed by McDaniel-aligned volunteers and election observers. The documents detail claims that election materials were destroyed or improperly handled and that vote-buying occurred.
Tyner said the committee will "have no choice but to recognize Chris McDaniel as nominee of the Republican Party" after it reviews the evidence.
"We're not asking for a new election, we're simply asking that the Republican Party actually recognize the person who won the runoff election," Tyner said.
McDaniel, a career trial lawyer, addressed the crowd as he would a jury and laid out his case, noting that "we saw the dirty tricks. We saw the dirty money that was coming from Washington."
He challenged the anger and frustration of his supporters and called out the "despicable acts of race-baiting" from people in his party and alleged that some of the "mistakes" during the runoff were "very intentional."
But McDaniel affirmed that the challenge is not centered on those emotions.
"We have to be dispassionate about the facts," he said. "The facts are on our side. The law is on our side."
The McDaniel campaign and its allies have spent the nearly six weeks since the runoff parsing county poll books, soliciting donations to fund an eventual legal challenge and offering $1,500 rewards to anyone who could provide evidence of voter fraud.
Bobby Morgan, communications director for the Mississippi Republican Party, called the challenge to the results of a federal election unprecedented.
Morgan said party officials are consulting with the organization's general counsel to determine how to handle the challenge.
Cochran campaign lawyer Mark Garriga slammed the McDaniel campaign's claims as "baseless" and said he looks forward to holding it to the burden of proof that the law requires."
"The filing of this challenge marks the point where this matter moves from an arena of press conferences and rhetoric into a setting where nothing matters but admissible evidence and the rule of law," Garriga said in the statement.
As Cochran made a last-ditch appeal to African-American voters ahead of the runoff, conservative groups hired former Justice Department official Christian Adams to train and oversee election observers to monitor polls and note questionable voter activity.
After 10 days of state party review, the campaign will likely shift its challenge to the courts, if necessary.
Regardless of the state party's actions, McDaniel campaign spokesman Noel Fritsch said the candidate would "in all likelihood, absolutely" file a suit in court.
The runoff winner will face Democrat Travis Childers in November. Mississippi is a reliably Republican state.