文摘
On May 24, 2001 United States Senator James Jeffords announced that he was switching from Republican to independent and would vote with Democrats on organizational matters (i.e. votes deciding party membership and majority party status), effectively taking majority party control of the Senate from the Republicans and giving it to the Democrats. This created an unusually well controlled quasi-experimental opportunity for learning about the role of parties in the Senate—it held most important variables constant while one variable, majority status, changed. We use roll call data to evaluate the probability of individual members of each party being rolled on Senate final passage votes, before and after the switch. We find that, contrary to conventional wisdom on the Senate, majority status is an important factor in Senate decision-making. Our results show that Republicans were more likely to be rolled after the switch than they had been before, and that Democrats were less likely to be rolled than they had been before. Keywords U.S. Senate Congress Parties Jeffords Natural experiment