Senate elections affect senators’ partisan behavior. Senators encounter incentives to
display party loyalty, but they must win reelection every six years to continue pursuing
ideological, partisan, and career-based goals in the U.S. Senate. Since most senators desire
reelection, they respond to credible electoral threats. Therefore, a senator’s electoral vulnerability
affects his party loyalty.
In this thesis, I examine the effect of elections on senators’ party loyalty through
interviews with Senate staffers, analysis of senators’ roll-call voting, and studies of four
senators’ careers. I conclude that senators facing competitive elections display less party loyalty
toward the end of their terms relative to their colleagues. I also find that the effect of elections on
senators’ party loyalty during the last two years of a Senate term parallel the effect of elections
on the party loyalty on House incumbents seeking reelection. Overall, senators’ perceptions of
electoral vulnerability influence how they represent their constituents.