Bill Keller waxes perplexedly about partisan state politics:  "…it feels as if every news cycle brings another seemingly random example of a state veering off the mainstream." Why? Keller briskly reviews the prevelant theories of partisanship–from gerrymandering, demographic sorting, to the urban-rural divide…and finds the possible answer in Samuel Abrams:

“People who participate in state and local government tend not to be representative of the masses at all,” Abrams told me. “They tend to be highly engaged political elites — 15 percent of the population who think they’re fighting this culture war. They’ll see an opening. They’ll see a judge, they’ll see a legislature that looks amenable to something, and they’ll try to push it through and build a groundswell around that.”

Hear here. On a side note one might question Keller's rather complacent assertion that division within Congress is easily explained by gerrymandering. At least some scholars,e.g., Brookings' Thomas Mann and William Galston,  see gerrymandering as a minor player. 

And when Keller states "When you look at voter registration or opinion polling, the fastest-growing political allegiance is not red or blue but “independent.”, this should be qualified:  the overwhelming majority of independents identify with one party or the other. (This gallup poll is typical, showing only around 10% of voters don't favor one party).  Or has something changed?