Emerging analysis explains how Trump campaign used Facebook's tools to target users

A former Facebook insider explains to Wired Magazine why it's almost certain that the Trump campaign's skill using the site's internal advertising infrastructure was more important in the 2016 US presidential election than Russia's troll farm was. The first was the ads auction; the second a little-known product called Custom Audience and its accompanying Lookalike Audiences. Like Google's equivalent, Facebook's auction has advertisers bid with an ad, an ideal user specification, and a bid for what they're willing to pay for their desired response; Facebook weights these bids according to how engaging the system thinks the ad is. During the election campaign, both Clinton and Trump bid for the same screen space in front of swing state voters - but Trump's content was more provocative and potentially cheaper, gaining him more ads for the same money. In addition, the rural users Trump targeted are likely to have been less expensive than the urban voters Clinton focused on. 

Custom Audiences takes lists of personal data submitted by campaign managers and collects matching users by searching the data Facebook has collected from both its own site and from the trails people leave in traversing the web. Lookalike Audiences then searches the friends of everyone in that Custom Audience to find people who "look like" those users to the system - perhaps they Like the same pages or choose to read the same News Feed content or interact with the same ads. The Russians also used these tools, but at a much smaller scale - they spent $100,000, compared to the Trump campaign's millions. 

Facebook has released a comparison of Trump's and Clinton's cost per thousand users, but for true transparency we need to see much more detail.

https://www.wired.com/story/how-trump-conquered-facebookwithout-russian-ads/
Writer: Antonio García Martínez
Publication: Wired