The roles and responsibilities of the minority leader are not well-defined. To a large extent, the functions of the minority leader are defined by tradition and custom. A minority leader from 1931 to 1939, Representative Bertrand Snell, R-N.Y., provided this "job description": "He is spokesman for his party and enunciates its policies. He is required to be alert and vigilant in defense of the minority's rights. It is his function and duty to criticize constructively the policies and programs of the majority, and to this end employ parliamentary tactics and give close attention to all proposed legislation."
What defines a large part of minority leader role?
tradition and custom