Democratic Sen. McCaskill takes sides in GOP primary

The unlikeliest would-be king maker in the Missouri Republican Senate primary isn't the Koch brothers or Karl Rove, it's Sen. Claire McCaskill, a one-term incumbent Democrat. 

McCaskill will face the winner of a primary Tuesday that pits a wealthy businessman with no political record against the state treasurer and a six-term congressman. 

She has taken the unusual step of running ads targeting each potential opponent ahead of the primary. One attacks businessman John Brunner, the front-runner, for not voting in some elections and slams his business losses. Another calls state Treasurer Sarah Steelman a business-as-usual politician beholden to special interests. And she dubs Rep. Todd Akin as the most conservative congressman in Missouri-hardly a drawback for a man running in a GOP primary in one of the reddest states in the country. 

Election experts say she appears to be rooting for Mr. Akin, in part because she trails him by the smallest percentage in the polls: A recent St. Louis Post-Dispatch poll found that in head-to-head matchups, Brunner would defeat her by 11 points, Steelman by eight points and Mr. Akin by five. 

The tactic reprises Sen. Majority Leader Harry Reid's effort in 2010 to promote Sharron Angle in the Nevada Republican primary by attacking her opponent, after he determined Ms. Angle would be the weakest challenger. Ms. Angle won the primary and Mr. Reid went on to defeat her in November. 

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