Blood informs a central racial ideology in the United States that has historically been used to racialize many different groups. American Indians (AIs) are the only population in the United States for whom the racial logic of blood remains codified as a means of conferring collective belonging. This article explores how AI blood quantum persists as both a race-making and nation-making instrument. I ask two research questions: How does blood quantum persist as a metric of tribal citizenship? Are tribal citizenship criteria connected to contemporary demographic, geographic, political, and economic forces? I first extend racial formation theory to describe blood quantum as a “racial project” in its use to both construct tribal identities in explicitly racial ways and determine access to political, social, and material resources. I also consider how the sovereign right of Native nations to confer tribal citizenship is evident in the observed variation among citizenship rules. Using data from more than 80 percent of AI Native nations in the contiguous United States, I employ a multinomial regression model to evaluate tribal citizenship variation. I have two central findings: (1) although tribal citizenship criteria are starting to depart from the racializing policies of the settler-colonial state, blood quantum thresholds remain particularly durable; and (2) variation in tribal citizenship criteria is meaningful by geographic region, tribal governance status, and Indian gaming. Against a backdrop of growing racial diversity in the United States, I discuss implications of the blood line on tribal citizenship boundaries and tribal sovereignty.

血液传达了美国的一种主要种族意识形态，该意识形态在历史上曾被用来使许多不同的种族种族化。美洲印第安人（AIs）是美国仅有的将血统种族逻辑编纂为赋予集体归属的手段的人口。本文探讨了AI血液量子如何既可以作为造种族的工具也可以作为造民族的工具而持续存在。我问两个研究问题：血液量子作为部落公民身份的度量如何持续存在？部落公民资格标准是否与当代人口，地理，政治和经济力量相关？我首先扩展种族形成理论，将血量量子描述为“种族计划”，以其以明确的种族方式构造部落身份并确定获得政治，社会和物质资源的途径。我还认为，在观察到的公民权规则之间的差异中，土著民族赋予部落公民权的主权权利如何体现出来。我使用了来自美国本土超过80％的AI原住民国家的数据，我采用了多项回归模型来评估部落公民身份的变化。我有两个主要发现：（1）尽管部落公民资格标准开始偏离定居者-殖民地国家的种族化政策，但血量阈值仍然特别持久；（2）部落公民资格标准的变化对地理区域，部落治理地位和印度博弈意义重大。在美国种族多样性日益增长的背景下，我将讨论血统对部落公民资格边界和部落主权的影响。