The volatility of median and supermajoritarian pivots in the U.S. Congress and the effects of party polarization

Abstract

Krehbiel’s (Pivotal politics, 1998) seminal work on pivotal politics in the US Congress emphasizes the importance of supermajoritarian rules and veto players in determining what bills can pass. We illustrate empirically that the volatility of the pivot points has increased markedly since the mid 1970s, and we link changes in pivot volatility to the degree of party polarization. In general, median and supermajority pivots shift considerably more than the overall mean and, when politics is polarized, the congressional median and supermajority pivots can change dramatically when a shift in control occurs. The relative volatility of median and supermajoritarian pivots varies with the degree of polarization and the extent to which there is continuity in party control. We develop a theoretical model to explain the nature of these relationships.