Senator Tom Harkin (D-Iowa) announced last Saturday that he will not seek a 6th term.  Harkin is 73 years old.  Iowa Democrat

Representative Bruce Braley is thought to be considering a run to replace Harkin.  On the Republican side, it appears (as has often been the case recently) that the endorsement could involve a fight between someone viewed as a moderate Republican versus someone who is viewed as a conservative Republican. 

Will Republican infighting help the Democrats retain the Harkin seat?  Time will tell. 

http://atr.rollcall.com/iowa-tom-harkin-to-retire-in-2014/

http://www.washingtonpost.com/blogs/the-fix/wp/2013/01/26/harkin-retirement-presents-gop-with-an-opportunity-and-a-test/