Uffda!

Not all of South Dakota subscribes to Rush Limbaugh type of thinking, but it is true that there may be more of it in South Dakota. I know enough people who are centrists, who are either registered as Democrats or Republicans (as for me, I am a registered Democrat but sometimes vote Republican-I vote for the person).
I am not sure how North Dakota is broken down politically by areas, but the central and western parts of South Dakota is very conservative with a couple of exceptions and eastern South Dakota is moderate (and many Republicans in this part of the state are generally more centrist and moderate in their view than their counterparts in rest of SD).
Eastern SD has areas where Democrats hold their own and this includes: very NE part of the state (Day, Roberts, and Marshall Counties), James River Valley (Huron, Aberdeen, Mitchell), Yankton, Vermillion, and Union County. Sioux Falls as a whole is a bellweather and split. Lincoln County and the portions of Sioux Falls in it (with some higher-end homes) has traditionally leaned Republican and has been that way for a long time.
South Dakota is traditionally a conservative Republican state but has been trending more in a centrist position in the past few years.