Amicus briefs provide information to Supreme Court justices from an outside party and can be influential for this reason. A state, or states, with an interest in a case may file an amicus brief for one party or another appearing in front of the Court. Research has shown that the more states who join on a brief, the more impact it may have with the Justices. If one or a few states has an interest in a case and wants their brief to be considered how do they get other states to join on a brief? If a state has no interest in a case, why would or wouldn't it join with a state who did have an interest? In this paper, I look at amicus briefs filed in the United States Supreme Court by states either when a state is a party or when they took interest in the case by filing a brief. When considering these cases (131 of them) the question I seek to answer is does partisanship determine who joins on an amicus brief? In order to answer this question, I focus on social network analysis of the cases and states who file for each case. This method allows connections to be made between states as well as identifying the central or influential actors within the network. I find that states who file the most briefs are not necessarily the most influential and if partisanship plays a role, it does so at the individual level and not at the whole network level.

Did interest groups influence the Supreme Court’s interpretation of federal economic regulatory authority under the Commerce Clause leading up to the Supreme Court’s 1937 reversal? Recent scholarship has begun a renewed study of this tumultuous era seeking alternative explanations for the Court’s behavior beyond the conventional explanations concerning Roosevelt’s court packing plan. I build on this literature by extending the discussion to the influence that interest groups may have had on the Court. I propose that interest groups served as a supporting and influential audience for the Supreme Court as the justices’ institutional legitimacy became threatened by both the political pressure and legal changes that the Court faced during this era. To test these theoretical assumptions, I compiled a dataset of Supreme Court cases using the U.S. Supreme Court Library Official Reports Database ranging from the beginning of the 1920 Supreme Court term through the end of the 1937 term. Cases were included if 1) the case had one or more filed amicus briefs; and 2) the questions and arguments in the case were based on the Commerce Clause or legislation that relies wholly or in part on the Commerce Clause. Applying a basic logit model, I find support for the assumption that amicus briefs influenced the Court by providing the justices with a supporting audience. To further test the influence of amicus briefs, I compare the arguments and information provided exclusively by amicus briefs in this group of cases to the Supreme Court majority’s opinions to test for similar content. Amicus briefs are considered influential if the Court included information exclusively from an amicus in their majority opinion. I find that in the largest number of cases, amici influenced the Court majority’s opinions in favor of their preferred litigant when they provide unique arguments and information. Consequently, I find moderate support for the influence of interest groups on the Court both externally by providing a supporting audience and internally by providing the Court with supporting information.