The Calculus of Cosponsorship in the U.S. Senate

We investigated why a legislator would be willing to vote “yea” on final passage of a bill but would choose not to cosponsor that bill. We tested a series of hypotheses regarding the cosponsorship decisions of individual senators, using a dataset that includes every major initiative that was introduced and received a floor vote in the Senate between 1975 and 2000. We found that senators are more likely to cosponsor bills when their preferences diverge from the Senate median but are closer to those of the bill's sponsor. Also, senators are more likely to cosponsor bills when they sponsor a higher number of bills overall, when they become more connected with colleagues, and when their constituents increase demand for legislation within particular policy areas. Senators are less likely to cosponsor bills if they received a higher percentage of the general election vote in their most recent election.