If the Dakota Territory was split east/west rather than north/south

[Cranberry]

East Dakota would probably be more Democratic also on presidential level, as the Democrats would definetly campaign there more.
But yes, locally the Democrats would do very well, similar to Western Minnesota/Northwestern Iowa.

[Cranberry]

While Republicans would win regularly in East Dakota on the Presidential level, local Dems would do really well on the statewide and congressional races. East Dakota would be very Scandinavian and Lutheran, sort of a more conservative and rural version of Minnesota. 

This is true, though things may be getting more partisan.

South Dakota was close enough in 1992 & 1996 that Clinton certainly carried the part east of the Missouri.  I believe that Obama lost East River to McCain by 3 points.

However, Bush & Romney handily carried both sides of the Missouri (even Sioux Falls isn't that liberal).  East Dakota gets even more conservative when the North Dakota part is added, and probably would not have even been carried by Clinton.

But again, I don't think he campaigned much in either of these areas, as he knew they would get Republican. If they were split East/West, he would definetely have campaigned more in the East; maybe that would have given him the East.