Propublica gives important background for understanding the alleged improper actions of the IRS:

In the furious fallout from the revelation that the IRS flagged applications from conservative nonprofits for extra review because of their political activity, some points about the big picture -- and big donors -- have fallen through the cracks. Consider this our Top 6 list of need-to-know facts on social welfare nonprofits, also known as dark money groups because they don’t have to disclose their donors. The groups poured more than $256 million into the 2012 federal elections. A century ago, Congress created a tax exemption for social welfare nonprofits. The statute defining the groups says they are supposed to be “operated exclusively for the promotion of social welfare.” But in 1959, the regulators interpreted the “exclusively” part of the statute to mean groups had to be “primarily” engaged in enhancing social welfare. This later opened the door to political spending.

1. Social welfare nonprofits are supposed to have social welfare, and not politics, as their “primary” purpose. 2. Donors to social welfare nonprofits are anonymous for a reason. 3. The Supreme Court’s Citizens United decision meant that corporations could pay for political ads, anonymously, using social welfare nonprofits. 4. Social welfare nonprofits do not actually have to apply to the IRS for recognition as tax-exempt organizations. 5. Most of the money spent on elections by social welfare nonprofits supports Republicans. 6. Some social welfare groups promised in their applications, under penalty of perjury, that they wouldn’t get involved in elections. Then they did just that.