Cruz has largely built his program out of his Houston headquarters, where a team of statisticians and behavioral psychologists who subscribe to the burgeoning practice of “psychographic targeting†built their own version of a Myers-Briggs personality test. The test data is supplemented by recent issue surveys, and together they are used to categorize supporters, who then receive specially tailored messages, phone calls and visits. Micro-targeting of voters has been around for well over a decade, but the Cruz operation has deepened the intensity of the effort and the use of psychological data. Cruz, a critic of excessive government data collection,...