This is the result of primaries decided as a result of gerrymandering. All aboard the crazy train!
That story is based on 2009 research: http://www.jstor.org/stable/25548144?seq=2
Admitting that gerrymandering isn't the problem puts the solution further out of reach, unfortunately. Generational change is slow and painful.
But the article does make good points of self selected voting districts resulting from people moving in and out of communities.