Bob Bauer has this post on More Soft Money Hard Law.  It begins:

Campaign finance jurisprudence is caught in the crosscurrents of formal doctrine and less clearly articulated judgments about the interests it is crafted to serve. One such judgment has to do with the “little guy”: the pamphleteer or small-scale political enterprise that raises and spends money to influence elections but whose activities have little or no corrupt potential and should not come within the regulatory grasp of the state. The Court has gone to considerable and inventive lengths to spare the little guy the dead weight of the rulebook, See, e.g. McIntyre v. Ohio Elections Comm’n, 514 U.S. 334 (1995) and FEC v. Massachusetts Citizens for Life, 479 U.S. 238 (1986) and it may have occasion in the near future to do more of the same. Because the doctrine is only roughly fitted to the purpose, the protection of the “little guy” has served the “big guys” well; an approach cobbled together on the fly for the smaller, more local enterprise has shielded the major political spenders.