Desks are important props. A recent candidate showed us a denuded tree in a dessert as a prop representing what would happen if his opponent were elected. A podium is a prop, or sometimes other people serve as props. All of these faces and their expressions are carefully planted in ads. A most common approach is to take the face of an opponent at its most unattractive and show that face as background for words written on the screen to indicate what awful things he has done.
Faces are probably a candidate's most direct conduit to creating feelings in viewers.
Every ad is designed to appeal to something in the viewer him- or herself. Insurance ads appeal to fears of disasters. Cosmetics appeal to personal ego. Many high-ticket products appeal to greed. Candidates appeal to feelings of patriotism, fears of such things as war, crime, loss of jobs, poor education for children and so on.