South Dakota map SC

SIOUX FALLS, S.D.— South Dakota Sen. Tim Johnson was expected to announce his retirement Tuesday, making the state the fifth where Democrats will have to defend a seat without an incumbent seeking re-election. The decision opens up a 2014 race that Republicans had already labeled as a top target to grab a seat.

Johnson, the chairman of the Senate Banking Committee, is expected to say Tuesday afternoon that he will not seek a fourth term in the Senate next year.

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Former Gov. Mike Rounds, a Republican, had announced plans last year to challenge Johnson, who still is coping with the constraints of a 2006 brain hemorrhage that left his speech impaired and limited his mobility.

By stepping aside, the 66-year-old Johnson, who had never lost an election, leaves South Dakota Democrats searching their youthful prospects for a potential successor.

“I believe South Dakota moves into the top slot as the most likely Republican pickup,” said Greg Strimple, a Republican pollster and past consultant to the National Republican Senatorial Committee.

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 Read More at OfficialWire . By Chet Brokaw.