In other words, 501(c)(4)s were intended to be allowed to spend NO MONEY on politics. However, a 1959 IRS regulation decided that "exclusively" (0%) really meant "primarily"(up to 49%), and in doing so they completely changed the spirit of law, which was not only illegal, but made the new law a nightmare difficult to enforce. Every single 501(c)(4) that has spent money on politics since 1959 has been in violation of the law passed by Congress — which means that the real law is almost guaranteed not to be enforced.
http://blogs.reuters.com/great-debate/2013/06/17/the-real-ir...