Jack and Ralph are involved in a power struggle. How does Jack undermine Ralph in front of the other boys?

At this point, however, some of the boys get distracted and spend time rolling rocks around the bridge. Ralph again gets frustrated and then asserts that it would be better to climb the mountain and rekindle the fire. He accuses the boys of losing sight of their original goal, finding and killing the beast. Contradicting Ralph, Jack states that he wishes to stay where they are because they can build a fort.