Although broadcasters in the US have had to maintain files on this sort of information for years, until 2012 it was only available in person, with members of the public forced to drive to a station's headquarters to retrieve the data. In 2012, however, the FCC forced TV broadcasters in America's 50 largest markets to upload the information online and in July 2014 expanded this legislation to cover all broadcasters. Since then, the FCC reports, more than 650,000 PDFs have been uploaded to its website, generating just under six million page views. After this "uneventful" implementation, the agency says it's ready to update the law again to cover cable TV, and satellite and broadcast radio.

These particular mediums are becoming more important than ever before to political campaigners. A report by The Economist from October last year noted that while political ads from the '70s and '80s tried to appeal to as many people as possible with a "shotgun approach," modern equivalents use "a sniper’s-rifle-with-telescopic-sights." This trend is partly being driven by access to new data, with cable TV operators selling information about subscribers' viewing habits to political campaigns. Although this data is anonymized, reports The Economist, it does include addresses, which can be matched to addresses from voter registrations.

With voter information like this, campaigns can make sure they're showing ads on cable TV channels with viewer profiles that best match their target audience. A study by ad strategy firm Echelon Insights gives the examples of the Golf Channel, where 93 percent of political ads are Republican, and compares it to Comedy Central, where 86 percent of the ads are for the Democrats. Stats like these show just how important targeted advertising has become, and the proposed legislation from the FCC should make it easier for anyone to investigate advertising sources on cable TV and radio.