If it ain't Gerrymandering, what is it?

Over at Wonkblog, there's a post up from John Sides showing some empirical evidence that would suggest gerrymandered districts are not the problem for polarization in Congress. Instead, the evidence would suggest party fealty leads to the differences between parties. It is pretty compelling, but I would add a few thoughts:

1) The evidence submitted doesn't distinguish what the votes were on, which is to say many votes are largely innocuous. In those instances, one would expect fealty to party because the individual may have little interest in the specific legislation. I would think there is some dilution of voting record going on here that might screw up the expected linear relationship.

2) Just because gerrymandering isn't the reason for polarization doesn't mean it's something we should ignore. Having so many "non-competitive" seats means it's easier for entrenched interests to capture a district and keep it. Does this, alone, increase polarization? No, but it does increase the ability to be loyal to one's party instead of one's constituents.

3) Towards the bottom of the post there's a mention of "leapfrog representation" which explains why, when a district flips, the congress person elected is often dramatically to the left or the right of his or her predecessor, instead of landing in the middle. If this is the case and gerrymandering isn't the cause, what is? I would suggest primaries are the issue.  Sides notes Seth Masket's work that suggests, "local party organizations have been captured by activists for whom ideological fealty is paramount." This would explain leapfrog representation and, to some extent, polarization.

The evidence put together is strong, but I think gerrymandering is half the issue. Primaries tend to contribute to polarization as well. Why else would conservatives make a PAC to fight other conservatives in primaries? The natural follow-on question would be to ask why Obama mentioned gerrymandering, but not primaries in his interview with The New Republic? I think it comes down to party fealty. Democrats have primaries so the President is constrained for criticizing it too loudly. I mean, if not for primaries would he be president?