Write Aaron's name on the staff of Levi. For there shall be one staff for the head of each fathers' house.
Numbers 17:3

Although there is always some kind of power sharing between the various offices in God's government, there is never competition for the same office. Although there are many pretenders, there is only one high priest, one king, and one supreme judge for the nation, and there is only one patriarchal chief of each tribe.