How Facebook tracks and profits from voters in a $10bn US election

Social network lets campaigns match profiles with political habits and contact info, as Silicon Valley influence becomes 'game-changer' for targeted ads

If you lived in north-east Iowa, the evangelical stronghold where the battle for the soul of conservative American politics will play out in person on Monday, and happened to have given Senator Ted Cruz's campaign your email address sometime in the last few months, you might find something especially appealing this weekend in your Facebook feed.

You might see, amid the family photos, a menacing video of Donald Trump talking about how "my views are a little bit different than if I lived in Iowa". LIKE ON ABORTION, blares the sponsored ad from Cruz's deep-pocketed, social media-savvy digital team. And you might wonder how this campaign managed, by paying Facebook, to differentiate between Trump's "New York values" and "OURS".