"Writing in the New Republic in 2014, Jonathan Zittrain, professor of international law at Harvard University, pointed out that, given the massive amount of information it has collected about its users, Facebook could easily send such messages only to people who support one particular party or candidate, and that doing so could easily flip a close election – with no one knowing that this has occurred. And because advertisements, like search rankings, are ephemeral, manipulating an election in this way would leave no paper trail."
"Are there laws prohibiting Facebook from sending out ads selectively to certain users? Absolutely not; in fact, targeted advertising is how Facebook makes its money. Is Facebook currently manipulating elections in this way? No one knows..."
Now we know.
See, now we know.