In a surreal speech late Tuesday night, Mississippi Senate candidate Chris McDaniel railed against his own state's party and vowed that his fight isn't over. He did not concede. (Jeff Simon/The Washington Post)

— Sen. Thad Cochran (R) narrowly survived the toughest election of his four-decade political career, holding off an insurgent tea party challenge from state Sen. Chris McDaniel in Tuesday night’s runoff after one of the most expensive and nasty primary campaigns of the year.

Cochran outperformed his vote totals from the primary election three weeks ago in many parts of Mississippi and he held a lead throughout the night. With 99.9 percent of precincts reporting, Cochran beat McDaniel 50.8 percent to 49.2 percent. They were separated by about 6,300 votes out of more than 375,000 cast.

Cochran relied heavily on boosting voter turnout in the runoff among not only mainstream Republicans but also black Democrats, whom his campaign and its allies aggressively courted in the final days of the campaign.

The contest between the entrenched Cochran and the more combative and youthful McDaniel divided the Republican Party here in one of the nation’s most conservative states and delivered a stinging blow to the tea party movement.

(The Fix: How Thad Cochran beat the tea party)

In a bitter and angry speech to supporters in Hattiesburg late Tuesday, McDaniel refused to concede and said, “we are not prone to surrender.” He cited “voting irregularities” and thundered that the “Republican primary [was] decided by liberal Democrats.”

“We’re not done fighting,” McDaniel vowed.

In nearly every Mississippi county, voter turnout was up over the inconclusive June 3 primary. But precinct totals show it was substantially higher in heavily African American areas. In the 24 counties with a majority black population, turnout increased by 39.4 percent, giving Cochran a big edge.

For example, in densely populated Hinds County, which includes the capital of Jackson, turnout was up nearly 50 percent over the June 3 primary and Cochran beat McDaniel by nearly 11,000 votes.

McDaniel, who had been backed by the money and manpower of the tea party movement, was hoping to channel the anti-establishment fervor of Mississippi Republican activists. He had the momentum heading into the runoff, but Cochran, a 36-year member of the Senate, gambled that stressing his seniority in Washington and his long history of procuring largess for this poor state.

Addressing cheering supporters in Jackson, Cochran said, “We all have a right to be proud of our state.”

“What we have tonight is a consensus for more and better jobs for Mississippi workers, a military force and the capacity to defend the security interests of the United States of America,” Cochran added.

In a tight runoff contest, Sen. Thad Cochran manages to eke out a victory against his tea party challenger, Chris McDaniel.​ (WLOX)

McDaniel and his allies responded to Cochran’s strategy of wooing blacks by dispatching operatives to monitor voters in Democratic areas — causing deep unease among civil rights activists in a state with a long and ugly history of racial politics.

National Republicans were watching the Mississippi race nervously, fearing McDaniel’s far-right positions and history of insensitive comments on matters of gender and race could give Democrat Travis Childers an advantage in this solidly Republican state and weigh down GOP candidates elsewhere.

The Mississippi Senate contest is the marquee race on this crowded June primary day, but elections are taking place in six other states as well.

In New York, another long-serving lawmaker, Rep. Charles B. Rangel (D), sought to fend off a younger challenger, state Sen. Adriano Espaillat, in a rematch of their close 2012 primary. First elected in 1970, Rangel is one of the most powerful African Americans on Capitol Hill, but he is struggling to hold his seat following a 2010 censure for ethics violations and demographic changes in his Harlem-based district.

In Oklahoma, Rep. James Lankford won the Republican Senate nomination, easily defeating state House speaker T.W. Shannon, who is half black and half Native American and was backed by Sen. Ted Cruz (R-Tex.) and some tea party groups.

Lankford, a member of the House leadership, is a Baptist minister and has a loyal following with religious conservatives from his days as the head of the country’s largest Christian youth camp in the nation. Given the state’s strong conservative tilt, Lankford, 46, will be a heavy favorite in the general election to fill the seat being vacated by Sen. Tom Coburn (R).

In Colorado, former congressman Bob Beauprez won the Republican nomination to challenge Gov. John Hickenlooper (D) this fall. Beauprez, the party establishment favorite, beat a field of candidates that included former congressman Tom Tancredo, a vocal anti-immigration activist.

And in Florida, Republican Curt Clawson, a businessman and former college basketball player, easily won a special election in the 19th Congressional District to succeed former Rep. Trey Radel (R-Fla.), who resigned after pleading guilty to a misdemeanor drug charge.

But many politicos were most focused on Mississippi, where Cochran, 76, and McDaniel, 41, have been locked in an increasingly vicious and bizarre internecine fight. In the June 3 primary election, McDaniel edged Cochran, but finished just shy of the 50-percent threshold, forcing the two men into Tuesday’s runoff.

The winner will face Childers, a relatively centrist former Democratic congressman who holds antiabortion views and voted against the Affordable Care Act.

As he visited with voters on Tuesday, Cochran resisted personally criticizing McDaniel. He instead delivered platitudes in a hoarse, sometimes barely audible voice, his rail-thin, dark-suited frame moving slowly. As state Rep. Brad Mayo (R) put it, Cochran’s style has “always been to use honey over vinegar.”

Cochran spent the morning campaigning along the Gulf Coast, an area dominated by military bases and neighborhoods devastated by Hurricane Katrina. His aid for both were core themes of his pitch highlighting the federal funds he has steered to Mississippi over the years.

Reaching out to black Democrats has been central to Cochran’s playbook in the closing days, with pamphlets, phone calls and field staffers canvassing majority-black communities in south Jackson and elsewhere. Cochran hopes blacks cross party lines to reelect a moderate Republican over McDaniel, a hard-charging fiscal hawk.

In Mississippi, which does not register by party affiliation, any registered voter can vote in the Republican runoff election as long they did not vote in the Democratic primary during the first round of balloting on June 3.

“We’ve spent a lot of time bringing a conservative message to black voters, as well as to white voters, the old and young, men and women,” said Austin Barbour who, along with Stuart Stevens, the chief strategist on Mitt Romney’s 2012 presidential campaign, is advising Cochran.

At Cochran’s satellite office in Hattiesburg, Stacy Ahua, 25, a black field organizer, managed a get-out-the-vote operation. She put out a box of Shipley doughnuts and distributed signs to a group of elderly Cochran backers.

“Some of our people forgot to come out for that first vote and we’ve really tried to get things moving,” she said. “I think everybody now understands the stakes, whether you’re Democrat or Republican, Catholic or Baptist.”

In response, the Senate Conservatives Fund, led by former Virginia attorney general Ken Cuccinelli (R), and other groups sent operatives to monitor the trickle of voters in Democratic areas. McDaniel staffers also were seen throughout Mississippi on Tuesday morning, notepads in hand, taking notes.

Jacob Creel, 20, a Marine reservist, was one of those poll-watchers, sitting inside a senior center and stepping out from time to time to make calls to his higher-ups about the kinds of voters coming by.

“We’ll be on the lookout all day to see if anything fishy happens,” Creel said as he paced near the parking lot.

NAACP leaders, wary of potential confrontations, sent their own monitors to Mississippi. Wayne McDaniels, president of Jackson branch of the NAACP, said, “If Cochran wins, it’s because of the black vote.” He said black Democrats “weighed the field and concluded that with Cochran, we know what we’ve got, and we like what we’ve got,” McDaniels added.

McDaniels said the NAACP had more than 200 people at the polls making sure black voters were not harassed, although he said there was one instance of voter intimidation in Canton.

Justice Department officials were also receiving updates about voting activity.

Former Mississippi governor Haley Barbour (R), a leading Cochran supporter, said Cochran’s focus on education issues and federal funding helped turn out voters who did not cast ballots three weeks ago. He also said Cochran’s temperament played a factor.

“Thad has always been a true gentleman, with no fist pounding or yelling, stomping around,” Barbour said. “People respond to that. They respect that kind of senator.”

McDaniel’s argument has centered not on Cochran’s voting record, but on his political temperament, with McDaniel frequently wondering aloud why Cochran shows “reluctance to engage Barack Obama.” He has said he would, promising to work alongside Sen. Ted Cruz (R-Tex.) and other tea party firebrands.

In the Pine Belt, a deeply conservative stretch of southeast Mississippi, frustration and fury with Cochran were evident. Outside a polling station near Hattiesburg High School, Birgil McLauren said with a heavy sigh that Cochran “hasn’t done a damn thing for 42 years, and six more years won’t make a difference.”

“I’m sick about hearing that he’s done so much,” said McLauren, 76. “If he’s done so much, why are we still the poorest state?”

The Mississippi race gained national attention this spring when McDaniel supporters were arrested in connection with taking an illicit photo of Cochran’s bedridden wife, Rose, who has dementia and lives in a nursing home.

The media attention has annoyed Cochran, whose campaigns have been relatively sleepy affairs since he first won his seat in 1978. Cochran over the weekend remarked to onlookers that he didn’t like his large tan-and-black campaign bus, calling it unseemly.

A bevy of GOP establishment groups, including the U.S. Chamber of Commerce, backed Cochran. On Monday, Sen. John McCain (R-Ariz.), one of the party’s most prominent foreign-policy hawks, campaigned for Cochran, a fellow Naval veteran. And popular former quarterback Brett Favre, a Mississippi native, appeared in an ad.

McDaniel has drawn support from national tea party groups as well as conservative stars, including former Alaska governor Sarah Palin, former senator Rick Santorum of Pennsylvania and Chuck Woolery, the original host of “Wheel of Fortune.”

Rucker reported from Washington. Ed O’Keefe and Sean Sullivan in Washington, and Philip Bump in New York, contributed to this report.