Thanks for the question! So we’re being asked for the author’s primary purpose. (D) says that this is to assess the claims made by disputants. This answer would have been best addressed by anticipating what the answer would be before looking at the answer choices. Remember, the author is generally trying to push a view of SCOTUS that is more positive than people have generally viewed it when it comes to tribal affairs. Choices (A)-(D) are all more neutral, whereas (E) is more of a persuasive type of answer and thus is correct. The primary purpose is to provide evidence to support a contention, the contention that is introduced at the beginning of the second paragraph.
Hope this helps! Feel free to ask any other questions that you might have.
