As I posted before, the reason SD voted for Bush but supports Daschle is that it is a small, poor state that needs power-players in both parties to get federal money. It's still a small, poor state -- what exactly has he done for them (besides get an exemption from the enviro's for the forests)? I heard somewhere that Daschle has built his support by providing excellent "constituent services" (rather like Teddy K here in MA).
The Farm Bill (aka farm welfare) is huge. Also the influx (or lack thereof) of federal money after the draught last summer was a big campaign issue.