There has been a lot of discussion about whether the "liberal" Congress will push President Obama's agenda to the left. Clearly, Republicans raised this fear in the
DW-NOMINATE scores, which are based on roll call voting records, run roughly from -1 to 1 where -1 is a very liberal score and 1 is a very conservative score. So to gauge how liberal a given House is, I simply compute the fraction of members with scores that fall beneath certain thresholds. The thresholds I chose were -.3, -.4, and -.5. To give the reader some context, Charlie Rangel and Nancy Pelosi score at approximately -.5, Rahm Emanuel clocked in just below -.4, and Dan Lipinski is just a little more liberal than -.3 (sorry that part of the ideological spectrum is devoid of household names).
The figure reports simple percentages within each of these categories from the beginning of the New Deal to the last congressional term. Obviously I do not have scores for new members and cannot project into next term. There isn't much need to go back before the New deal, because the pre-New Deal Democratic caucuses were small and overwhelmingly southern.
The results are somewhat striking. The 110th House was not only the most liberal since the New Deal, but the percentage of liberals has been increasing for some time. The patterns do not vary much with the threshold used.
At first blush, this may seem surprising. But it is worth remembering that the proportion of liberals is directly related to both the percentage of Democrats in the House and how liberal the Democrats are. Before 2006, the percentage of Democrats had been on the historically low side. But because the party has been losing its more moderate and conservative members from the South, it has become a considerably more homogeneous and liberal party in the House.
So what can be said about the incoming 111th House. Unless the Democratic party's 20 seat gain in the House is composed of almost exclusively moderates and conservatives (highly doubtful), the next House will be the most liberal in history.