Robert G. Boatright,Michael J. Malbin, and Brendan Glavin have a new paper titled "Independent Expenditures in Congressional Primaries after Citizens United." The abstract:
This paper examines how Citizens United affected the balance of power in “outside” groups in congressional primaries through 2014. After the decision, critics predicted massive independent expenditures (IEs) by large corporations, while supporters saw it shifting the balance toward insurgent outsiders. While IEs were up, we expected and found neither of these effects. Instead, the paper documents: (1) an unsurprising increase in the number of (and decrease in the focused coordination among) IE groups; (2) a substantial change in the types of groups that wield power, with an increase in
the importance of ones tied to party leaders and decrease in the power of factional outsiders; and (3) the emergence of single-candidate PACs, with the most significant growth among those allied with incumbent office holders. The heightened power of mega-donors with issue agendas, underwriting new organizations, is important and well documented. But the changes supporting visible party leaders and incumbents could also have important systemic consequences over time.