He was one of the signers of the second Treaty of Fort Laramie in 1868[1] and remained a bitter opponent of further American settlement, ridiculing Spotted Tail and other Sioux leaders upon their return from a mission to Washington, D.C.

One of the principal leaders at the Whetstone Indian Agency, located along the Missouri River, where most of the Brulé and Oglala bands had gathered, Big Mouth gained increasing support for his stance among members of the tribe.

Some hours later, Blue Horse came to agent Poole's office and told him that he felt so sad over the death of his great and good brother that he would have to wash off the paint he had put on his face for the feast the day before and begin mourning.

[4] Blue Horse, Big Mouth's twin brother, was pressed to avenge the murder, but chose the path of non-violence and instead moved with his Wagluhe band to another locality.

Nonetheless, Red Cloud continued to work with Spotted Tail in delegations to Washington, D.C. to protect tribal lands, enforce broken treaties and preserve Lakota culture.