Thune beat Daschle. Barely.
Johnson beat Thune (congressional IIRC) in 2002.
South Dakota is always a close call anymore.
Thune/Johnson was a Senate race in ‘02, with Johnson winning by @ 500; Thune/Daschle, also a Senate race, in ‘04 had Thune winning by @ 4500. No landslides there, tho I imagine Thune would do better in a re-election race than in a challenge to the very well funded Senate Minority/Majority leader.