Mississippi primary could be key in battle for Senate

Mississippi mud slinging

Mississippi voters go to the polls Tuesday for a primary election that represents the most surprising wild card in the partisan fight for control of the U.S. Senate.

The race pits Republican Sen. Thad Cochran, seeking a seventh term at age 76, against tea party-backed state Sen. Chris McDaniel, 41. National GOP leaders, as well as major office holders in Mississippi, back Cochran in the belief that if he wins the Republican nomination, he'd be a shoo-in for re-election. If McDaniel wins, Democrat Travis Childers, a former congressman, might have an outside chance of winning in this most conservative of states.

That could prove critical to Republican hopes. The GOP needs to gain six seats to recapture a Senate majority. With 11 Democratic seats in play, they have plenty of targets.

Sen. Thad Cochran, R-Miss., second from left, greets patrons at Windy City Grille as Mayor Chip Johnson looks on in Hernando, Miss., May 30, 2014.
Tom Williams | CQ Roll Call | Getty Images

But the Republican path gets much steeper if they lose any of the three vulnerable seats they already hold. In two of them, Georgia and Kentucky, Republican primaries have eliminated tea-party challengers that GOP strategists believe might have helped Democrats to unexpected winsas occurred in five different Senate races in the 2010 and 2012 elections. Mississippi is the one 2014 primary contest left with the potential to do that again

That risk has grown in recent weeks due to a bizarre incident roiling the Mississippi fight. Supporters of McDaniel entered a nursing home, snapped photos of Cochran's wife, who suffers from dementia, and posted them online.

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The incident triggered felony chargesand attack ads from both sides. "Had enough?" asked a Cochran spot. McDaniel has countered by saying neither he nor his campaign was involved, and accused Cochran of smearing him.

Though the incident may have disgusted voters, it has not dramatically undercut McDaniel's support. Polls show the two candidates running nearly even. Intra-party battles are often unpredictable, given their relatively low turnout. About 300,000 voters are expected to decide the race.

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Beyond their differences in age, the two candidates represent a portrait in stylistic contrast. The genial Cochran, in line to become chairman of the Appropriations Committee if Republicans regain control, has consistently brought home federal dollars to Mississippi, the poorest state in the union. The more acerbic McDaniel accuses him of excessive cooperation and willingness to tolerate big spending.

—By CNBC's John Harwood