Dynamics of Congressional Loyalty: Party Defection and Roll-Call Behavior, 1947-97

I seek to determine whether or not political parties have significant independent effects upon the roll-call behavior of their members. Taking advantage of a natural experiment, I analyze the roll-call behavior of those members of the House and Senate from 1947 to 1997 who changed party affiliation while in office. Using data from the 80th to 105th Congresses, I find that Democrats who become Republicans, for instance, start to vote like Republicans at the time they cross aisles. This finding is consistent with the claims made in a growing literature that emphasizes the partisan aspects of congressional organization, and it supports the contention that party plays a direct role in determining members' roll-call behavior.