Iowa is an enigma. It's full of corn and farmers, yet it has a distinctive democratic lean and doesn't seem to be trending to the right. What makes Iowa more liberal than other farming states?
Iowa is not understood well by people not from the Midwest. It's not some land of endless fields of corn. It has cities where the population actually lives, and while they aren't large enough to give rise to white flight and hordes of ugly suburban conservatism they are large enough to have a somewhat cosmopolitan and liberal culture. There's no reason to expect places like Des Moines, Iowa City, Cedar Rapids, Waterloo and Davenport to vote Republican.
The whole movie
Cedar Rapids is based on this thing, Ed Helms' character plays someone from rural small town Wisconsin who goes on a business trip to Cedar Rapids and is overwhelmed by the "big city" culture.