I am not familiar with this issue, but it raises a question: just where, exactly, is the United States border? If it happens to run through the reservation, then too bad for them; we have sovereignty over our own borders. If in fact our border takes a turn in some direction to account for this reservation, then we simply build the wall on our border, and voila, all of the reservation ends up on the south side of the wall.
We have a sovereign agreements with the reservation, we have sovereign agreements with Mexico.
Set Jeff Sessions upon these agreements and who has broken them