The cornerstone of the US campaign finance system is transparency, which is ensured by frequent and detailed campaign finance disclosure. By law, the official committees of candidates for federal office, party committees, PACs, and Super PACs are required to file regular reports to the FEC disclosing the funds they raise and spend on the campaign. The reports contain a list of all donors who donated over USD 200, along with their address, employer and job title. The FEC makes the reports public on its website within 48 hours after their receipt.

However, the growing importance of outside groups, which can  incur unlimited independent expenditures as long as they do not coordinate with candidates’ campaign committees, have raised concerns as regards transparency of third-party campaign spending. Indeed, the so-called 501(c) non-profit organizations do not have to disclose their donors as long as campaign activity is not their primary activity and have been used, especially since the 2012 general elections, as vehicles to circumvent disclosure requirements.[1] During the 2012 election cycle, overall outside spending amounted to a total of USD 1.3 billion. According to the Center for Responsive Politics,[2] of USD 1 billion spent by outside groups, USD 300 million was spent by the 501(c)s.[3]