RETIREMENT. This week the New York Times reported that Joseph Lieberman (I-CT), who caucuses with the Democrats, has been speaking with previous contender Linda McMahon, a Republican campaigning for her party’s nomination for Lieberman’s seat, drawing the ire of many establishment Democrats. Lieberman’s retirement and that of other members of Congress this year raises this question: how does the replacement of incumbents (and particularly moderates) by new members affect the polarization of the parties in Congress? University of Texas political scientist Sean Theriault finds (ungated) that the replacement of moderates by more ideologically extreme members has driven polarization:
As southern Democrats, the bulk of whom were in the middle third of the ideological continuum, died, lost, retired or otherwise vacated their seat, they have been, for the most part, replaced by conservative Republicans. Quite simply, when extremists replaced moderates, the ideological middle disappeared and the parties diverged.