Jeremy Waldron studies what Aristotle intuited:
Virtue theorists believe that the disposition to act and react courageously or honestly is deeply entrenched in a person's character. As Appiah describes their position, a virtue is supposed to be something that "goes all the way down," enmeshing itself with other aspects of character, equally admirable, and affecting what a person wants out of life, her conception of happiness, and her views of other people. Are there such virtues? Well, the psychologists that Appiah has read report that character traits do not exhibit the "cross-situational stability" that virtue presupposes.
DiA summarizes Waldron's argument and applies his reasoning to politicians.