A same-sex marriage amendment, depending on the text, might serve to incorporate Indian tribes into the federal union as the third sovereign. The Constitution has not been amended to incorporate Indian tribes into the federal union, rendering their place in Our Federalism uncertain and unpredictable. A same-sex marriage amendment that applies to limit or expand tribal authority to recognize or authorize same-sex marriage could constitute an implicit recognition of Indian tribes as the third sovereign in the American system of federalism. Even an amendment that excludes mention of Indian tribes may have something to say about Indian tribes as the third sovereign.
Matthew L.M. Fletcher, Same-Sex Marriage, Indian Tribes, and the Constitution, 61 U. Miami L. Rev. 53 (2006).