Interest Group Lobbying and Partisan Polarization in the United States: 1999-2016

The lobbying activity of interest groups has been overlooked as a contributing factor to legislative party polarization in the United States. Using bill-level data from Congress and three state legislatures, I show floor votes on bills lobbied by more non-profit interest groups are more polarized by party. The state legislative data demonstrate the robustness of the relationship between lobbying and polarization, showing it is not an artifact of party agenda control, salience, or bill content. Increased lobbying from these groups in recent years helps explain high levels of partisan polarization in Congress and an uneven pattern across the state legislatures.