Call it a do-over. After months of bitter fighting in Mississippi between the Tea Party-backed insurgent and the defiant Establishmentarian, the GOP primary for the US Senate seat will have one last, three-week hurrah. Chris McDaniel barely edged out 38-year incumbent Thad Cochran in the voting but narrowly missed the 50%+1 vote mark needed to win the nomination. A runoff will take place between just the two top candidates on June 24:

Locked in a race that won’t end, Mississippi Sen. Thad Cochran and tea party-backed challenger Chris McDaniel pointed toward a possible June 24 runoff after battling to a near-draw Tuesday in a primary that underscored Republican differences.

Unofficial returns from 98 percent of the state’s precincts showed McDaniel with slightly over 49 percent of the vote in a three-way race and Cochran with slightly less. It takes a majority by one candidate to avoid a runoff.

“For too long, we’ve been silent. For too long, we sat still. For too long, we let them have their way with us,” McDaniel told supporters late Tuesday in a slap at the Washington establishment.

“It’s looking like a runoff,” conceded Rep. Gregg Harper, addressing a crowd of Cochran supporters.

It’s going to cost some outside groups even more cash in a race where they’ve already spent general-election levels of money:

Already a savagely personal race, the duel between Cochran and activist state Sen. Chris McDaniel could now drag on until the next vote on June 24 and present national Republicans with a dilemma: Whether to continue supporting the senator and tearing down McDaniel at the potential cost of damaging the party’s eventual nominee.

Outside groups have already spent more than $8 million in the Republican Senate primary, an extraordinary sum in a small state that rarely hosts competitive federal elections. Cochran and his allies have assailed McDaniel as a bumbling snake-oil salesman and finger-in-the wind opportunist who’s out of touch with Mississippi’s priorities. McDaniel and his campaign have attacked Cochran’s record of voting for federal spending, accused him of being soft on President Barack Obama and raised not-so-veiled questions about the senator’s age.

First, let’s not worry too much about any damage to the eventual nominee, for three reasons. One, it’s difficult to imagine that this race will get any more “savagely personal” than it already has. Two, there will still be four months for whatever damage is done to dissipate in a very Republican-friendly environment. And three, each of the two Republicans drew about twice as many votes as all Democrat votes combined in their primary last night, with about a 4:1 ratio between the two parties. The general election won’t be an 80/20, but it won’t be 51/49, either.

A runoff only really looks like bad news for Thad Cochran. McDaniel established his credibility as a state-wide candidate with his plurality over Cochran last night, and as Allahpundit noted last night, Cochran’s standing as an unassailable institution has crumbled. His inability to best McDaniel last night may have some Mississippi voters who supported the incumbent last night wonder whether it’s better to make a change now that is obviously inevitable, while those few who voted for someone other than the top two finishers are already looking for a Cochran alternative. The runoff will probably still be relatively close, but don’t be surprised to see McDaniel win by more than 51/49, either.