Here is the opinion in United States v. Smith.

An excerpt on blood quantum:

The government presented sufficient evidence of Smith’s Indian blood to satisfy Bruce’s first prong. We have held this requirement satisfied by as little as 1/8 (12.5%) Indian blood. See Maggi, 598 F.3d at 1080; Bruce, 394 F.3d at 1223. Here, the government presented evidence that Smith has 25/128 (19.5%) Assiniboine and Sioux blood, well in excess of the 1/8 we approved in Bruce and Maggi. We acknowledge that Smith’s § 2255 motion attached a letter from the Fort Peck Tribes Enrollment Office stating that Smith “does not meet the required blood quantum of 1/8 for Associate Membership [in the Fort Peck tribes], nor 1/4 Full Enrollment.” But this evidence was not presented at trial, and even if it had been, a rational trier of fact could have chosen to credit the more specific, higher figure established by the government’s evidence.

An excerpt on the defendant’s relinquishment of tribal membership:

We recognize that Smith relinquished his tribal enrollment in 1996. This decision does not definitively show, however, that Smith or the tribe ceased to consider Smith an Indian person. See Cruz, 554 F.3d at 850 (holding that Bruce requires an analysis of Indian status from the perspective of the individual as well as from the perspective of the tribe). A tribal investigator, Tom Atkinson, testified he had known Smith for most of his life, that Smith had lived on the reservation that entire time and that, as far as Atkinson knew, Smith held himself out to be an Indian person. A rational jury could have concluded that because Smith was once formally enrolled in the tribe and continued to hold himself out as an Indian even after his enrollment ended, both Smith and the tribe continued to view Smith as an Indian despite his unexplained decision to relinquish his formal enrolled status.