Martin Gilens, Shawn Patterson Jr., & Pavielle Haines in APSR:

Despite a century of efforts to constrain money in American elections, there is little consensus on whether campaign finance regulations make any appreciable difference. Here we take advantage of a change in the campaign finance regulations of half of the U.S. states mandated by the Supreme Court’s Citizens United decision. This exogenously imposed change in the regulation of independent expenditures provides an advance over the identification strategies used in most previous studies. Using a generalized synthetic control method, we find that after Citizens United, states that had previously banned independent corporate expenditures (and thus were “treated” by the decision) adopted more “corporate-friendly” policies on issues with broad effects on corporations’ welfare; we find no evidence of shifts on policies with little or no effect on corporate welfare. We conclude that even relatively narrow changes in campaign finance regulations can have a substantively meaningful influence on government policy making.