The person most commonly regarded as the foremost authority on the subject is a linguist named Ives Goddard, who studied the word extensively. He writes that the word was originally intended as a term of respect, but became derogatory in the early 1800s. It was, for a time, used to describe scalps. More to the point, however, is its current, accepted context in which it is generally regarded as a racial epithet.
The racial epithet is given further derogatory prowess when considering both the historical context of genocide, and that of the team's location- our nation's capital.