What protects the rights of the accused by requiring that laws be applied fairly?

DUE PROCESS protects the rights of the accused by requiring that laws be applied fairly.
Due process refers to the legal obligations of the state; it is a constitutional requirement that prevents the government from treating its citizens in an abusive manner. Due process of law include the standard procedures which the court must observe at all time during its proceeding and other liberty interests that the law must not infringe upon.

An elector in the electoral college.