JACKSON, Miss. — It appears that the show must go on.
Hours after the polls closed, Republican incumbent Sen. Thad Cochran and insurgent challenger state Sen. Chris McDaniel had yet to capture enough of the vote Tuesday in the Mississippi primary to win the GOP nomination for the Senate seat outright, setting up a June 24 run-off.
Rep. Gregg Harper, a Cochran supporter, emerged around 11:15 p.m. to address the hundreds that turned out for Mr. Cochran’s election night party in a hotel ballroom, telling them that “it is looking like a run-off.”
With 96.5 percent of the precincts counted, Mr. McDaniel held a razor-thin 49.5 percent to 49 percent edge over Mr. Cochran, with a third candidate snagging less than 2 percent.
In other closely watched races, former South Dakota Gov. Mike Rounds won the Republican nomination for Senate — and instantly became the favorite to pick up a seat for his party in its drive to capture a majority this fall.
In Iowa, Republican state Sen. Jodi Ernst was declared the winner in a crowded race, earning the right to oppose Democratic Rep. Bruce Braley in the fall for a seat long in the hands of Democrat Tom Harkin.
Republicans eyed another fall pickup opportunity in South Dakota, where Democratic Sen. Tim Johnson has chosen to retire, and Mr. Rounds easily eclipsed his rivals for the GOP nomination. Rick Weiland, making his third try for a seat in Congress, was unopposed by other Democrats.
Democrat Sen. Cory Booker had no competition for renomination in New Jersey, and four Republicans sought to oppose him in the fall.
Republican governors winning renomination included Robert Bentley in Alabama and Dennis Daugaard in South Dakota. Both are heavily favored to return to office in the fall.
All Eyes on Mississippi
But the main event Tuesday was in Mississippi, where Mr. Cochran’s supporters had hoped the incumbent could avoid a run-off later this month, fearing that it would favor his tea party-backed opponent, in part because of the intensity of McDaniel’s supporters.
“I think a run-off probably plays to McDaniel’s advantage, probably just because of low turnout,” said Henry Barbour, who created the Mississippi Conservatives super PAC, which spent nearly $1.7 million on Mr. Cochran’s behalf.
The winner of the run-off will face former Rep. Travis Childers, who easily won the Democratic nomination and could benefit from an extended battle on the Republican side.
The latest campaign finance reports show that Mr. Cochran has $681,000 left in the bank, while Mr. McDaniel had $237,000.
Tea Party Challenge
The Mississippi primary battle follows primary contests in Kentucky, where Senate Minority Leader Mitch McConnell thumped his tea party-backed challenger, and in Georgia, where the establishment-favored candidates — Rep. Jack Kingston and businessman David Perdue — advanced to a July 22 runoff, besting a couple of tea party rivals along the way.
The Mississippi GOP Senate primary was viewed as the insurgent wing’s best bet to recreate some of the magic of the 2010 and 2012 primary election seasons, when several seasoned Republicans were knocked off.
The result ensures that the ongoing civil war between the GOP establishment and the party’s grass-roots will continue.
Matt Kibbe, president of FreedomWorks — which has a super PAC that put $286,000 into the race for the challenger — said he expects the Washington establishment to continue to fight against Mr. McDaniel.
“If we add Chris McDaniel, that puts more and more pressure on leadership to behave conservatively,” Mr. Kibbe said. “I think they are going to double down. I think it is going to get more hostile because they are losing big bucks, they are losing their positions of privilege — and how would you react? You’d fight back.”
Mr. Cochran, 76, closed out his campaign reminding voters that the state has benefited from his seniority and his ability as a member of the Senate Appropriations Committee to steer federal dollars back to Mississippi — including in 2005, after Hurricane Katrina devastated parts of the state.
Mr. Cochran enjoyed the support of the state’s top elected officials, including Gov. Phil Bryant and Sen. Roger F. Wicker.
He also had the backing of the U.S. Chamber of Commerce, which spent $500,000 on the race, and former Gov. Haley Barbour, who has warned that ideological purity is the “enemy of victory.”
But Mr. McDaniel, 41, said that Mr. Cochran was part of the problem in Washington.
He blamed him for being on the wrong side of battles over spending, Obamacare and immigration, and vowed to fight for the nation’s founding principles alongside the likes of rising conservative star Sen. Ted Cruz of Texas.
“The conservative movement has compromised way too often,” Mr. McDaniel said at a campaign stop Monday.
Mr. McDaniel has support from former Pennsylvania Sen. Rick Santorum and former Alaska Gov. Sarah Palin as well as a slew of conservative groups, including the Club for Growth, which spent almost $2.5 million on the race.
The race turned nasty last month after McDaniel supporters were arrested for illegally taking pictures of Mr. Cochran’s wife, Rose, who suffers from dementia, at her nursing home.
The McDaniel campaign has not been linked to the episode, and the candidate has denied any wrongdoing.
But the episode dominated the headlines for weeks, and the Cochran campaign and its allies kept the issue front and center by running ads about the incident.
Ford O’Connnell, a Washington-based GOP consultant, said that Mr. McDaniel sent a message with his strong showing.
“Cochran has thrown everything at McDaniel including the kitchen sink and there is no question McDaniel is standing his ground,” Mr. O’Connell said. “Without Rose-gate this might likely already be over, because it increased turnout.”
Mr. O’Connell also said that Democrats are looking to expand the map wherever they can and are more likely to invest in the race if Mr. McDaniel wins the race.
“They are going to look for every opportunity they can to try to force Republicans to pick up seven seats,” he said. “So they could start to marshal resources if McDaniel won, but it is still a long shot even if McDaniel is the nominee.”
Before the results were counted, Brad Chism, a Mississippi Democratic consultant, said that Mr. McDaniel does come with some baggage — including a stint as a provocative radio talk show host — that could haunt him in the November election.
“If McDaniel wins, then national Republicans will have to deal with his neo-Confederate remarks, his lengthy series of sound bites from his talk radio program — in addition to the other headaches [of] the traditional Republicans making peace with the more radical wing of the party,” Mr. Chism said.
Several of the voters filing into the Chastain Library in Rankin County on Tuesday said that they liked Mr. Cochran, and had voted for him in the past, but that it was time for some new blood.
“The man needs to retire,” said Henry Horton, 72, “Forty-two years? It is time for a change.”
Bobby Peoples, who was working a precinct Tuesday for Mr. Cochran, said the incumbent deserved another term because the state benefits from his seniority and his ability to build bridges on Capitol Hill.
“I disagree with the politics of not trying to come to some kind of compromise,” Mr. Peoples said. “We need to have somebody that is going to have our point of view, not somebody who is going to be an outcast in D.C.”
Asked whether he thought Mr. McDaniel could lose the seat in the general election, Mr. Peoples said, “I do not.”
“If Chris McDaniel beats a six-term incumbent, he is absolutely going to beat Travis Childers,” he said.