A correspondent read my recent note on the limited influence of the median voter and writes:

My understanding of median voter theorem is that each election has its own median voter, and that the median voter’s influence is limited to the outcome of that election only. I don’t understand, then, why the graph in your post is evidence that the median voter has little influence. It seems to me that there are two elections being considered in that graph, with two different median voters. The graph appears to consider “moderation” to be having a moderate voting record in Congress, but it seems to me that the median voter in Congress is likely quite different from the median voter in any particular Congressional district. The power of the median voter in Congress, it seems to me, is to affect the outcome of Congressional votes, not to improve his own chances for re-election, which are determined by his proximity to the median voter in his district. Thus, I’m not sure why we would expect moderation, as measured by the median Congressional voter, to translate into electoral success, which we would expect to be determined by the median district voter.

My reply:

Yes, there are two medians: the median congressmember (or maybe the 60th-most-liberal senator), and the median voter in any congressional district or state.

I definitely agree with your point about the median congressmember. As I wrote in the blog entry you cited, “Certainly the median congressmember is important: by definition, it’s that marginal vote you need to get a majority. But where do the median congressmember’s positions come from?”

What our graph showed was that it’s not as important as you might think for a congressmember to be near the median voter in his or her congressional district. This was the point that I was focusing on, because this was the point being made by various pundits: Ben Nelson can’t be too liberal because he’s representing the people of Nebraska; or, Many Democrats in Congress represent moderate-to-conservative districts, so therefore they can’t be too liberal; or, There’s no way Olympia Snowe can get away with voting against Obama all the time, given that Maine is a strongly Democratic state; etc. These arguments have some force–Ben Nelson, Olympia Snowe, etc., certainly could lose their seats–but the evidence shows that the benefits from moderation aren’t huge.