McLendon is a former soldier during World War I, and he was even decorated for valor for commanding troops in France. He seems to embody authority in many ways: his feet set wide apart as he stands, his body "poised easily" and his glance, "hot [and] bold." He is not the kind of man who is used to opposition; he is obviously much more accustomed to being obeyed, and even his body language conveys authority and power. When he enters the barbershop, he barks at everyone present, asking if they are all just going to sit around and let a black man rape a white woman. He yells at the only person to question him, asking, "What the hell difference does it make? Are you going to let the black sons get away with it until one really does it?"
In other words, he does not care if a black man is actually guilty of the crime of raping a white woman; by simply punishing a black man for the rumor, he believes that he can prevent another black man from actually committing this crime. He does not care about justice, then: he cares about power.
McLendon carries a gun, and he seems intent on using it against one black man in particular: Will Mayes. Though the barber argues that Will Mayes would not have done such a thing, even arguing that the alleged victim might have made it up or encouraged an actual, consensual sexual encounter, McLendon is not at all interested in hearing the truth. The barber argues, later, that Will Mayes would have run off if he had done what they accuse him of, and his continued presence in town must mean that he's innocent. However, McLendon does not care. He wants to commit some violence against Mayes, and nothing will dissuade him from it.
In the end, McLendon is even revealed to be a domestic abuser. In addition to being a terrible racist and murderer, he orders his wife around and hits her when she appears to disobey him. He thrives on power, whether it is over black people or over women; he seems to have no humanity left.