The article [1] and video [2] below shed some light on the "how". The video is mentioned directly in the article. The text explains how highly sophisticated targeting was deployed by the Trump campaign, and how it differed from Clinton's campaign. Highly informative.

[1] http://motherboard.vice.com/read/big-data-cambridge-analytic...

[2] https://www.youtube.com/watch?v=n8Dd5aVXLCc