SD Sen. Johnson announces official retirement

FILE - In this Oct. 14, 2009 file photo, Sen. Tim Johnson, D-S.D., is seen on Capitol Hill in Washington. Democratic officials say Johnson intends to announce his retirement on Tuesday, March 26, 2013, a decision that gives Republicans a prime opportunity to pick up a seat in 2014. (AP Photo/Haraz N. Ghanbari, File)

SIOUX FALLS, S.D. (AP) — Democratic U.S. Sen. Tim Johnson of South Dakota says he's retiring at the end of his term, but he stopped short of giving a specific reason.

The 66-year-old said at a news conference that he wants to spend time with his grandchildren. He also thanked people for their support during his "health crisis."

Appearing in his hometown Tuesday, Johnson made it official he will not seek a fourth term. Lingering effects from a 2006 brain hemorrhage have slowed his speech and caused him to use a motorized scooter.

The move gives Republicans one of their best chances to gain a seat and regain control of the Senate.

The only announced Republican candidate so far in the GOP-trending state is Mike Rounds, who was governor for two terms after being elected in 2002.