I just received a very thorough analysis of the election from a South Dakota high school history teacher which was great. Keep the thoughts coming. Also, here's another factor I don't think anyone has mentioned before from yet another reader:
Another factor that I feel was significant in the Daschle defeat was the Hutterite vote. I helped to register the people from our colony (most of whom had never voted before), and I know they voted for Bush/Thune/Diedrich. I also heard that there were several other colonies who allowed their people to vote for the first time.
For the uninitiated, there are number of communal colonies of German-speaking (at least until recent years) Hutterite farmers in South Dakota.