Well, that's what makes Cambridge Analytica so good, they have the data, and they're cheap. They just needed to target undecided voters in swing states, and through trawling Facebook data, they knew which voters to influence, and how to influence them, because they also have their psychological profiles. And how do you target them? By posting Facebook ads where you define your "target market" so narrowly that it basically hits individuals.
Actually, I suspect what makes Cambridge Analytica "so good" is that (big data aside) it was revealed just today: they use bribes and sex workers to entrap politicians, amongst other illegal techniques...
