Here, on SSRN.

The abstract:

The question whether Congress may create legal classifications based on Indian status under the Fifth Amendment’s Due Process Clause is now reaching a critical point. Critics claim the Constitution allows no room to create race or ancestry based legal classifications. The critics are wrong. 

When it comes to Indian affairs, the Constitution is not colorblind. Textually, I argue, the Indian Commerce Clause and Indians Not Taxed Clause serve as express authorization for Congress to create legal classifications based on Indian race and ancestry, so long as those classifications are not arbitrary, as the Supreme Court stated a century ago in United States v. Sandoval and more recently in Morton v. Mancari. 

Should the Supreme Court reconsider those holdings, I suggest there are significant structural reasons why the judiciary should refrain from applying strict scrutiny review of Congressional legal classifications. The reasons are rooted in the political question doctrine and the institutional incapacity of the judiciary. Who is an Indian is a deeply fraught question to which judges have no special institutional capacity to assess.