Why does Lean Elk take over Looking Glass' position as one of the chiefs of the Ne-mee-poo in the novel, Thunder Rolling in the Mountains?

Looking Glass was the leader of the warriors, guiding the Ne-mee-poo's wartime strategy and attempting to take his people to the land of the Crows where he believes they will receive help. However, he is wrong because the Crows refuse to help the Ne-mee-poo, and he further disgraces himself by ignoring many warnings and premonitions among his men who believe that the Blue Coats will soon attack. The men's premonitions were correct, and Looking Glass's failure to act on their recommendations causes many Ne-mee-poo to be killed. He loses the respect of his peers and therefore Lean Elk takes over in his role.