How does the beast's appearance weaken Ralph's leadership capability?

Shortly after Samneric claim that they saw the beast, Ralph and Jack lead a search party throughout the island, and the hysteria begins to affect the boys' perceptions and behavior. Even though Ralph is the elected chief, Jack assumes a leadership role during the expedition, because he is in charge of the hunters. Shortly after Ralph, Jack, and Roger witness the beast for themselves on the top of the mountain, Jack attempts to usurp power and starts his own tribe at the other end of the island. Unlike Ralph, Jack promises to protect the boys from the beast and has a stellar reputation as the most efficient hunter in the group. In the midst of the hysteria surrounding the beast, Jack is able to manipulate the boys into believing that only he is capable of killing it and defending them. He calls Ralph a coward and allows his prowess as a hunter to speak for itself. Jack also manipulates the boys' fears by leaving the severed pig's head as a sacrifice to the beast and speculating on its supernatural powers. While Jack's popularity grows as a powerful hunter and masculine leader, Ralph quickly loses his authority and becomes an outcast along with Piggy and Samneric. Overall, the beast's presence allows Jack to gradually usurp power by disguising himself as the most qualified person to protect the boys from the threatening monster.

By Chapter 6, when the beast from the air arrives terrifying Sam and Eric, Ralph's authority as leader of the boys is already shaky. Jack is already challenging Ralph's system of rules, and disorder and chaos threaten. To assert his leadership, Ralph states his position as chief and sets off alone in search of the beast, leaving Jack and the bigguns behind. To Ralph's surprise, Jack follows him, but Jack decides to do this to keep up his reputation as a brave hunter.
Later, at the end of Chapter 7, Jack taunts Ralph into looking for the beast again. They find it, the thing that bows, and Ralph is so terrified by what he sees that he runs away, and it is implied that Jack does too. In Chapter 8, when the boys meet and Jack takes the conch and speaks, he uses this incident to discredit Ralph and to weaken his authority. Then Jack goes on to explain that Ralph isn't a hunter, and therefore is less equipped to lead than Jack himself. All of these events weaken Ralph's position as leader.