Anthony Johnstone has posted this draft on SSRN (forthcoming George Mason Law Review).  Here is the abstract:

Notwithstanding its secondary holding that there is “no constitutional impediment” to requiring disclosure of those who fund independent campaign expenditures, the case for campaign finance disclosure is not as clear as Citizens United would suggest. The Supreme Court tends to assume rather than explain the “informational interest” that is cited to support disclosure. Without a clear constitutional justification, that interest does less than it might to define the means and ends of disclosure policy, and to defend that policy against constitutional challenge.

This article excavates the existing constitutional foundations for campaign finance disclosure, and roots the informational interest in a republican idea of corruption as factionalism that predates the narrow transactional conception of corruption dominant in contemporary political speech debates. That idea, explicated by James Madison in the Federalist and embodied in the Constitution, motivates an antifactional informational interest both broader and narrower than is presently conceived. It is broader in the sense that informing voters through disclosure of a wide range of interests in political campaigns is critical to the full function of the Constitution’s antifactional machinery. It is narrower in the sense that the interest is in disclosing interests—factions—and not other information that voters may find valuable for other reasons. Rooted in the broad importance and narrow purpose of antifactionalism, a deeper informational interest may better serve the First Amendment’s republican values without violating its libertarian command.

An antifactional reconception of the informational interest may help solve, or at least clarify, several puzzles in the First Amendment doctrine of campaign finance law. First, targeting interests instead of individuals for disclosure relieves the latent tension generated by the Court’s embrace of political anonymity in McIntyre. Second, understanding corporations as factions provides a sounder basis on which to distinguish corporate political actors from others after Citizens United. Third, the republican concern about faction offers a coherent rationale for drawing lines between domestic and foreign political speakers, whether the “foreigners” come from a different district, a different state, or a different country. Fourth, by recognizing corruption as the private benefit of factions at the expense of the general welfare, rather than the personal benefit of an officeholder at the expense of a faction, the antifactional interest calls for at least as robust a disclosure system for issue advocacy as it does for express advocacy of candidates.