In relation to people, they are the simplest group in a population. They have the simplest opinions, the simplest views and the simplest lifestyles. They are the unsophisticated (which is not correlated to the amount of happiness they have - in fact, living a simple life may make you even more happy than living a sophisticated one). Because these people do not think as much as a sophisticated person, they tend to be more naive and more gullible to gut feelings, and the ingrained culture and social laws that are around them. Their trust is easily earned.
In terms of politics, this can be taken advantage of when politicians use their persona and the gut feelings of their audience to gain followers, even when their policies and views might be to their disadvantage.
Those GOP candidates like to target the lowest common denominators in each state because it's easy followers for them. I mean, who would follow Rick Santorum because of a sweater vest?