The statistics of targeting individual voters with specific messages, as opposed to messaging that went to whole groups, began in the U.S over a decade ago with the Democrats. Political targeting is now an established business, or at least a discipline within the broader realm of political consulting. By 2016, the Republicans had surged well ahead, by stealth. The Trump campaign worked together with a special team* of Facebook analysts (Trump supporters) to implement a sophisticated campaign to target individual voters with Facebook ads. Parscale attributes Trump’s victory to this Facebook ad campaign.

The Trump campaign did not just use a standard set of static ads, but rather a constantly evolving smorgasbord of ads whose key elements were constantly changing in response to user involvement – over 50,000 different ads per day. Digital manager for Trump, Brad Parscale, described in a 60 Minutes interview how Facebook helped them set up algorithms that would change different aspects of ads, depending on how individual user reacted. Which makes you more likely to click – an American flag, or a scary picture of Hillary Clinton? Whichever works for you will be shown again to you in the future.

But suppose you don’t click at all? Even if you don’t click, a sophisticated statistical uplift model, coupled with the constant testing of multi-arm bandits, can help decide whether you get the flag or the picture of Hillary, based on a predictive model.

A predictive model like that requires information about individuals, which can come from Facebook. Facebook has an enormous amount of data on its users – Dylan Curran, writing in the Guardian, reported that his Facebook data amounted to roughly 600MB, which is roughly 400,000 Word documents.

In case Facebook restrictions on data use proved too restrictive, the Trump campaign also hired Cambridge Analytica, which, at the time, had an app that allowed it to scrape not just its users’ Facebook data, but also the data of their Facebook friends. At first this was relatively unnoticed, but blew up into a major controversy nearly a year later when Facebook claimed that scraping friends of friends data was was not permitted. But it remains unclear whether the embedded Facebook team at the Trump campaign took advantage of this extra data.

*Facebook also had a similar team available for embedding with the Democrats, but they said that the Democrats failed to take advantage of it.