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The Mississippi GOP Senate primary, the nastiest this cycle, is officially headed for a runoff, possibly just a three-week extension of more intraparty warfare.

Backers of six-term incumbent Sen. Thad Cochran now need to make the decision about whether to keep the fight up against tea party challenger state Sen. Chris McDaniel when he might very well end up as their nominee.

Former Mississippi Gov. Haley Barbour is backing the pro-Cochran super PAC Mississippi Conservatives and, in an interview with ABC News, said he would absolutely in no way back down from the fight.

"No, ma'am, not one bit," Barbour said. "We are not going to let a bunch of people from Washington or New York dictate who represents Mississippi in the U.S. Senate."

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In a nail biter of a race, McDaniel came out on top Tuesday with 49.5 percent of the vote to Cochran's 49 percent. Less than 1,400 votes separated the two when counting finally was completed this afternoon. Mississippi requires a threshold of 50 percent to declare a winner so there will be a runoff June 24.

Barbour called the race so far the "most negative, nasty primary I have ever seen," noting the nursing home scandal and saying he can't imagine the runoff could "be that bad again."

Barbour, who is forbidden from coordinating directly with the Cochran campaign because he is backing the super PAC, stressed that he believes McDaniel supporters are from out of state "special interest groups."

"Club for Growth or FreedomWorks, the groups that spent the vast majority to attack Cochran, those guys couldn't care less about Mississippi," Barbour said. "They wouldn't know Pascagoula from Pontotoc.

"They are all in it for a national agenda where they have to get a scalp in order to stay in business. They are 0 for 2014 and Cochran is their last chance," Barbour said, adding that if they don't get one win "people will quit giving them money and they will have to get another job … It's the outside gunslingers vs. the Mississippians.

"At the end of the day who can be more effective in the U.S. Senate for the next six years and there is no doubt in our mind," Barbour said, adding there's "no doubt" in the minds of Mississippians who voted for Cochran Tuesday either.

Barney Keller, spokesman for conservative anti-tax Club for Growth, responded to Barbour's comments saying, "We know this is a tough time for Haley Barbour. He's supposed to be all powerful, but he's losing a race in his own backyard, and his Washington lobbying fees will take a big hit when he no longer has a Mississippi senator in his back pocket."

"It would be nice if Haley Barbour chose to put our country's fiscal interests above his fiscal self-interest," Keller added

Barbour, in a more specific look at what the strategy of the pro-Cochran super PAC might be, mentioned an Associated Press article that notes McDaniel said in April that the federal government should have no role in education, including paying for it.

"The word 'education' is not in the Constitution. Because the word is not in the Constitution, it's none of their business," McDaniel said at an April 10 campaign event. "The Department of Education is not constitutional."

Barbour said this is just one of several "issues" that make the differences between McDaniel and Cochran "very plain."

"Mississippi is the poorest state in the country," Barbour said. "If every penny that goes to special education comes from the federal government, federal money goes to our universities and community colleges, are you going to vote for a guy who wants to do away with that? I don't think so."

McDaniel's campaign did not immediately respond to a question about whether he still supports that position.

There was over $8 million in outside money poured into this expensive race from both sides and the majority, about $5 million, did go to boost McDaniel. His supporters say they too will eagerly keep up the fight, looking at how Cochran wasn't able to beat McDaniel outright and also a track record this season of incumbents falling in runoffs, including 91-year-old Ralph Hall in Texas last month.

The tea party fervor is on McDaniel's side and that it likely to stay just as hot in the next three weeks, although it does give an extra three weeks for the especially nasty nursing home scandal to continue to develop. In April, a McDaniel supporter sneaked into a nursing home where Cochran's bedridden wife has lived for over a decade with dementia.

Once inside, the McDaniel supporter proceeded to secretly film the wife of the three-term congressman-turned-senator and then put the video online. McDaniel disavowed the act and says he has no relationship with the conservative blogger. Four people were arrested.

The tea party group FreedomWorks has already spent $350,000 on the race and will spend a "few hundred thousand more" on the runoff with their president, Matt Kibbe, promising to "double down" their efforts in the next three weeks.

John Bruce, chairman of the political science department at the University of Mississippi, says there are two possible scenarios in the runoff, including "wide open warfare" and there will be "complete saturation like Ohio in a presidential election, it will be bombardment." The next scenario is Cochran sees his "institutional support quietly soften a bit" as they weigh going after someone they might need to back in the general election.

Of course, Barbour is one of Cochran's most powerful backers and he has promised to stay in the fight.

"Today people are calculating what is the right thing to do," Bruce said. "If it continues it will be crazy. The television [ads] for Mississippi have been crazy. In presidential years we hardly see a commercial and we have been besieged by almost all outside groups."

Mississippi GOP Chairman Joe Nosef also said today both campaigns are "taking a fresh look at what they've been doing and whether that's correct to continue to do in the specific context of turning people out for a run off or if they should change what they are doing."

Nosef said Cochran's campaign believes Tuesday night was a "wake-up call" to Magnolia State Republicans.

"Believe it or not a lot of people until last night didn't think Sen. Cochran could ever be challenged in any serious way because he served the state for so long," Nosef, who has remained neutral in the primary, said, adding that those people who were surprised Tuesday night are the people whom the Cochran campaign is hoping to turn out.

Nosef says the Cochran camp believes their support will pick up now that voters have seen it is "possible for him to lose."

As for how negative it will be, Nosef said it would "certainly surprise" him if the two campaigns "went totally negative for the next three weeks."

"I think it is safe to say the McDaniel people were very confident going in to last night and the Cochran people were more cautious, but they view [the runoff] as a more positive development and see it as a second chance," he said.

Despite Mississippi's red-state political heritage, some political commentators have said that if McDaniel were to be victorious coming out of Tuesday's primary, then former Rep. Travis Childers, the Democratic Senate nominee, would have had a better shot at winning the general election. Throughout the primary, the Mississippi Conservatives super PAC pounded McDaniel and recently highlighted some controversial statements he made during his time as a talk radio host, saying McDaniel would "embarrass" the state.

But Nosef says it's the bruising battle, which will now continue, that will make the general election more competitive.

"Because we've had this race, obviously, we are going to have a tougher general election than we would have had because we have had no general election," Nosef said, adding they are "ready for the challenge" and will focus on telling voters who are "upset after the primary and may sit out the general election or vote for the Democrat, why it does not advance the causes they believe in."

ABC News' Elizabeth McLaughlin contributed to this report.