Cambridge Analytica claims to be able to predict voters’ personalities and manipulate their behavior using 5000 data points. Kaiser said the firm had purchased every available data set in the U.S.
This type of demographic profiling has been going one for decades with regard to consumer spending habits (e.g. data mining Visa purchases or use of a grocery store "reward" card). It's been used to accurately predict marriages, pregnancies, job changes, college graduations, and other major life events triggering spending that can be targeted.
Should come as no surprise that such data mining and psychological profiling is (and has been) used in politics to persuade voters in general and convention delegates.