Interest Group Activists and the Polarization of State Legislatures

Theories in campaign finance research suggest that interest group contributions moderate, and individual contributions polarize, state legislators. However, interest groups are comprised of individuals, and public opinion data suggest that group-affiliated individual donors are more politically active and have especially extreme attitudes. This article investigates the relationship between group-affiliated donors and legislative polarization in the U.S. states. In recent elections, individual contributors have grown more closely affiliated with activist organizations, such as environmental and anti-abortion groups. Contributions from these group-affiliated contributors predict legislative extremism at least as well as overall contributions from interest groups, individual donors, party committees, and party-affiliated individuals. Using a novel data set of state legislative primary dates, results suggest that this relationship may be concentrated in the nomination process. Although the potential for endogeneity merits caution, the findings complicate theoretical firewalls between organizations and individuals in research on parties, interest groups, and campaign finance.