Why do interest groups contribute so little, despite legal limits? This article argues that internal constraints on Political Action Committees (PACs), specifically partisan preferences of donors, provide a crucial explanation. Access-seeking PACs rely on voluntary donations from affiliated individuals like employees.

The Partisanship Constraint: When these PACs donate to candidates of the opposite party, they alienate potential donors who share those partisan views. The findings show that donors withhold contributions when PACs cross partisan lines.

This claim is supported by two studies: First, a difference-in-differences analysis reveals clear evidence of donor gatekeeping at access-seeking PACs based on political leanings.

Second, an original survey combined with experimental work involving corporate PAC donors demonstrates they know exactly how their PACs allocate resources across parties. This knowledge extends to understanding the operational mechanics and strategic implications of partisan constraints.

Why It Matters: The research shows donor partisanship directly constrains access-seeking PAC fundraising capacity. These findings shift our understanding of interest group influence, revealing an internal barrier that limits campaign contributions even when legal restrictions allow more. This provides fresh insights into political money dynamics.