Ellen Aprill has posted this important draft on SSRN (forthcoming University of Illinois Law Review On-Line).  Here is the abstract:

On November 2, 2017, the House Ways and Means Committee released its proposed tax reform legislation. It includes a provision amending the provision of the Internal Revenue Code, sometimes called the Johnson Amendment, that prohibits charities, including churches, from intervening in campaigns for elected office, at risk of loss of their exemption under section 501(c)(3). Under the Ways and Means proposal, as later revised and passed by the House, organizations exempt as charities under section 501(c)(3) would be permitted to engage in campaign intervention if “the preparation and presentation of such content . . . is in the ordinary course of the organization’s regular and customary activities in carrying out its exempt purpose and . . . results in the organization incurring not more than de minimis incremental expenses.”
If such legislation becomes law, the IRS and the Department will be faced with the difficult task of giving guidance as to the meaning of “regular and customary,” “de minimis,” and “incidental.” It would likely have to address whether donations could be earmarked for campaign intervention so long as they were within the organization’s de minimis limit and involved regular and customary activities. Whatever rules are announced are sure to be controversial and complicate enforcement of the prohibition for campaign intervention that is more than de minimis. Given the lack of IRS resources and controversy regarding its attempts to regulate political activities of exempt organizations, the IRS may well hesitate to take action against possible violations.
However these terms are defined and enforced, a de minimis exception raises significant issues that demand attention in an era of what Professors Eugene Volokh and Richard Hasen have called “cheap speech.” These are issues that require consideration whether or not a de minimis exception is adopted in the current tax reform legislation.
After giving background on the Johnson Amendment, this essay discusses the impact of any de minimis exception regarding campaign intervention in the age of cheap speech. It concludes that the availability of cheap speech may have undermined the most common constitutional justification for the prohibition – that the government has no duty to subsidize speech – such that a new approach to limiting the political speech of charities is needed.