Explaining Restraint from Filibustering in the US Senate

While much has been written about the increase in filibustering over the past two decades, there has been very little discussion of the fact that, even today, opponents of legislation that could be filibustered often do not exercise this institutional right – even when doing so means the difference between defeat and passage of the measure. This study seeks to explain why legislation opposed by a cloture-preventing minority is not always filibustered. Based on a broader look at the strategic environment facing senators, this study lays out six specific hypotheses. Analysis of data from 1947-98 provides substantial empirical support for most of these hypotheses, demonstrating that the strategic calculations behind the decision to filibuster are complex and multifaceted. In particular, this study finds that for legislation on which opponents have a clear incentive to filibuster, restraint is more likely to occur when the workload is light, when parties are not polarised, when the president favours the measure, when opponents' cloture-preventing margin is slim, and on minor legislation.