Johnson's office has said he moves through the Capitol on the motorized scooter so he can move quickly and conduct Senate business, not because he cannot walk under his own power. He often leaves the scooter behind as he heads into meetings and stands under his own power when speaking on the Senate floor.
Johnson's health hasn't slowed his ascent in the Senate. He because chairman of the Senate's powerful Banking, Housing and Urban Affairs Committee in 2011.
Rounds said he doesn't expect the campaign to begin in earnest until early 2014, but he had to declare his candidacy now to begin building the campaign organization and raising the money needed to challenge an incumbent.
His campaign said his accomplishments as governor included beginning construction of an underground science laboratory at the former Homestake gold mine in the Black Hills, boosting tourism, increasing research at state universities, creating college scholarships, working with the congressional delegation to save Ellsworth Air Force Base from closure in 2005, and helping to make South Dakota a business-friendly state with low taxes.
Associated Press Writer Henry C. Jackson in Washington contributed to this report.
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