FILE - In this Sept. 21, 2011 file photo, Sen. Claire McCaskill, D-Mo. listens on Capitol Hill in Washington. Republican voters in Missouri chose among three candidates on Tuesday, Aug.

 

              FILE - In this Sept. 21, 2011 file photo, Sen. Claire McCaskill, D-Mo. listens on Capitol Hill in Washington. Republican voters in Missouri chose among three candidates on Tuesday, Aug.
FILE - In this Sept. 21, 2011 file photo, Sen. Claire McCaskill, D-Mo. listens on Capitol Hill in Washington. Republican voters in Missouri chose among three candidates on Tuesday, Aug. 7, 2012, who during the primary campaign touted their conservative credentials in the hopes of taking on Democratic incumbent Sen. Claire McCaskill in November, a contest considered crucial to the GOP's efforts to regain control of the U.S. Senate. (AP Photo/Manuel Balce Ceneta, File)