Changing Public Policy: The Impact of Public Opinion, Antiwar Demonstrations, and War Costs on Senate Voting on Vietnam War Motions

A new approach to the study of legislative change enables us to deal directly and quantitatively with questions about how long-term changes in public policy come about. The approach is applied to the aggregate change of mind by the U.S. Senate as it moved from support of the Vietnam war to opposition from 1964 to 1973. Substantively, cumulative war costs, public opinion, and antiwar demonstrations all had significant effects on Senate roll call outcomes, but they were so highly intercorrelated that their separate effects could not be disentangled. In addition, demonstrations taking place in the months before a vote had a slight positive impact on the number of dovish votes received by motions. The 1970 invasion of Cambodia seems to have led to a significant turning point in the way the Senate dealt with the war. The general strengths and weaknesses of the new approach are assessed. It opens a new area to statistical inquiry and generates a number of novel questions that should lead to additional research.