The former Republican governor's decision to run for Democratic Sen. Tim Johnson's seat was not seriously in doubt -- he's already formed an exploratory committee, he's planning three stops around the state Thursday, and close friends told reporters he was in the race. 

Johnson has yet to say whether he will seek reelection, but he is considered one of the more likely retirements of 2014. If he doesn’t run, former congresswoman Stephanie Herseth Sandlin would likely be the Democrats' top choice to replace him.