Dark Money. (Short version).

Another day another scheme IRS hearing held by, Darrell Issa, chairman of the hearing IRS investigation scam. The IRS investigated both Liberal and Republican groups. Now, the reason the IRS was looking into them in the first place is because of the dark money sliding through the tax exempt status as a bribe of sorts. Thus, funneling money to political parties, in an effort, to influence elections and policies.

In order to qualify and maintain 501 C 4 tax exempt status an organization must use at least 60% of its donations toward 'social welfare. Helping the poor...etc.,

However, this is not happening. Instead, they are funneling millions of dollars into the Republican Party. Of course, this is a clear violation of their tax exempt status, and a misuse of the status.

Source.
1). Cenk Uygur. (4 April 2014). The Dark Money Of 'Social Welfare' Groups Is The Real IRS Scandal. The Young Turks.https://www.youtube.com/watch?v=tTEdQNiRxQk