Don't just blame political candidates for all the glossy flyers cluttering your mailbox, for the in-your-face television and radio advertisements and calls at home that interrupt your dinner. Chances are, much of that electioneering is being paid for by one of an untold number of advocacy groups.

These groups, formed under section 527 of the Internal Revenue Code, primarily were involved in issue advocacy and weren't permitted to tell the public explicitly to elect or defeat a particular candidate – until the Supreme Court's Citizens United decision in 2010. Now, they may engage in the full range of political activity, including asking the public to vote for or against a would-be officeholder. Swift Boat Veterans for Truth, which ran "issue ads" critical of Democratic presidential nominee John Kerry's Vietnam War record in 2004, was one of the more well-known 527 groups in the pre-Citizens United years. Some organizations, including labor unions, use 527 accounts to support or oppose state and local candidates and contribute to other committees.

In addition, some large, national party-connected groups are formed as 527s, such as the Republican State Leadership Committee and the Democratic Governors Association.