A Supreme Court case about jurisdiction in an obscure murder has huge implications for tribes. On the morning of June 22, 1839, the Cherokee leader John Ridge was pulled from his bed, dragged into his front yard and stabbed 84 times while his family watched. He was assassinated for signing the Cherokee Nation’s removal treaty, a document that — in exchange for the tribe’s homelands — promised uninterrupted sovereignty over a third of the land in present-day Oklahoma. That promise was not kept. Sixty-seven years later, federal agents questioned John’s grandson, William D. Polson. They needed to add him to...