According to Trende:
[T]he point here isn’t that gerrymandering hasn’t had any effect on party polarization. It is just that the effects are likely very small. What’s really happened, more than anything else, is that conservative areas of the country have, at least for now, become extremely reluctant to elect conservative or moderate Democrats, while liberal areas have largely given up on liberal or moderate Republicans. This has resulted in party caucuses that are increasingly made up of ideologues, and has made political compromise difficult. If there’s anyone to point the finger at, it’s ourselves.
Enten adds:
The Senate shows … that the sharp upswing in polarization we see today is largely the product of natural voting patterns. And these manifest themselves on the state level without any gerrymandering. Texas put Ted Cruz in the Senate not because someone redrew Texas’ state lines, but because Texas voters became, on average, more conservative.
The Dish 