I guess we’re not explaining this well enough.

Dave Weigel:

I enjoy the new, #slatepitchy argument that gerrymandering is overrated as an issue, and that it doesn’t influence whether members moderate their votes or not, but sequestration’s putting that to a test.

Kevin Drum:

Hold on a second. Who’s saying that? The argument I’ve heard making the rounds lately is that gerrymandering is probably responsible for a fairly modest change in the number of House seats Republicans won last year…But who’s been saying that gerrymandering has no effect on whether members feel any need to moderate their votes or their rhetoric? What have I missed?

What both of these normally astute writers are missing is that gerrymandering (drawing district lines for political reasons) is only one reason for safe seats.

Why are there safe seats? Lots of reasons, including:

* Geographic distribution of partisans. If Democrats and Republicans live in different neighborhoods, or different cities, or are differently drawn from urban, suburban, and rural areas, then you’re very likely to get lots of safe partisan seats unless districts are very specifically drawn to prevent it.

* Partisan voting. As voting by party increases, any Republican in a Republican seat becomes safer, as do Democrats in Democratic seats.

* Incumbency. Even Republicans in Democratic districts can be safe if incumbency advantages are strong enough.

* Information. To the extent that, say, Republicans get most of their political information from the GOP-aligned partisan press, they’re very likely to support their current Republican Member of Congress. Note that the old “neutral” press tended to be extremely incumbent-friendly to their Congressional delegations.

* Gerrymandering. Be careful, though. The kind of gerrymandering that tends to create safe seats, especially for the majority party, is bipartisan gerrymandering — the kind in which incumbents from both parties cooperate to draft lines that protect all incumbents. See California, 2002-2010, for a famous example. Partisan gerrymandering tends to yield more seats for the majority party at the cost of each of those seats being relatively less safe. However, partisan gerrymandering, to the extent it’s successful, should make the “victim” party have safe seats; the idea is to pack as many of the minority party into as few seats as possible, but to use majority voters more efficiently.

So: yes, gerrymandering has effects, although they’re less impressive than many think. But when it comes to safe seats, gerrymandering on the whole won’t be a major factor, and partisan gerrymanders in particular shouldn’t (overall) produce more truly safe seats for the majority party. Of course, it may produce some; one of Weigel’s example is a Member whose seat was made safer through partisan redistricting. On the other hand, however, perhaps without that gerrymander (and I haven’t looked into what happened in this case) the seat wouldn’t have been a safe Republican seat at all; maybe it would have been a Democratic seat.

Generally, this reminder: for whatever reason, people really, really, really like attributing effects to gerrymanders. So if you come across one of these, by careful: it’s very possible that something else is really at work.

[Cross-posted at A plain blog about politics]

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Jonathan Bernstein is a political scientist who writes about American politics, especially the presidency, Congress, parties, and elections.