Another cool chart from the Monkey Change which compares the ideological distribution of the electorate to that of the House and Senate. All three curves are bimodal, but the voters clump closer to the center than do the members of congress. Were I David Broder I would argue that this shows the wisdom of the masses and the baleful influence of special interests in pushing party leaders to extreme positions, but realistically it probably reflects the fact that members of congress are much better-informed about politics than are average voters, and therefore members of congress tend to have more coherent ideological viewpoints.
The other interesting point is that the electorate seems, on the whole, slightly left of where the congress is. The "trough" of the voters' bimodal distribution is to the left of the House and Senate troughs, and the left peak in the electorate is substantially higher than the right peak but that's not true in the congress. You should probably expect congress to be somewhat to the right of the public thanks to the fact that the current gerrymander mostly favors Republicans and the apportionment of the Senate tends to overrepresent conservative parts of the country.
Matthew Yglesias is a former writer and editor at The Atlantic.