FILE - Newly elected senator for South Dakota Tim Johnson and wife Barbara wave at cheering supporters at a celebration in Sioux Falls, S.D., Nov. 5, 1996. (Frank Robertson/The Argus Leader via AP, file)

FILE - Sen. Tim Johnson, D-S.D., is pictured in Arlington, Va. in this Aug. 26, 2005 file photo. (AP Photo/Charles Dharapak, File)

FILE - In this Oct. 14, 2009 file photo, Sen. Tim Johnson, D-S.D. is seen on Capitol Hill in Washington. (AP Photo/Haraz N. Ghanbari, File)