Mississippi state Sen. Chris McDaniel is challenging Sen. Thad Cochran. National Journal

The biggest Republican primary of 2014 looks like it's going into overtime.

Neither Sen. Thad Cochran nor his tea-party-backed primary challenger, state Sen. Chris McDaniel, appeared able to secure the majority needed to win their party's nomination in Mississippi on Tuesday night. That triggers a June 24 runoff, extending their nasty campaign — and the accompanying expensive barrage of television advertising.

With 94 percent of the vote counted, McDaniel was ahead of Cochran by about only 1,000 votes. A third candidate, little-noticed real-estate agent Thomas Carey, took just enough to play spoiler for both candidates. 

But McDaniel's team was confident on Tuesday night. He entered the race last October before Cochran had announced his reelection bid, and the state legislator quickly drummed up support from the Club for Growth, the Senate Conservatives Fund, FreedomWorks, and an assortment of other conservative groups. Cochran was planning to retire toward the end of the primary, he told The Washington Post, but he answered pleas from establishment-minded supporters to run again as McDaniel and allies attacked him as a symbol of pork-barrel spending profligacy.

Not surprisingly for a race that became the preeminent showdown between the Republican establishment and the tea party, it attracted heavy spending from outside groups. According to the Center for Responsive Politics, they spent more than $8 million in the race, and more money will likely come in over the next few weeks as both sides try to keep their supporters engaged for the quick runoff. Cochran would be the first Republican senator to lose renomination this cycle, and his finishing below 50 percent in the initial primary won't do anything to deter his opposition.

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