An overlooked memo from the Interior Department's top lawyer could play a critical role in the fate of the Dakota Access pipeline, and the Trump administration is considering erasing it.

Obama-era Interior Solicitor Hilary Tompkins late last year issued a formal legal opinion outlining reasons the government should conduct further study before granting final approval for the controversial oil project.

The 35-page memo says the existing environmental assessment for Dakota Access suffers from fatal flaws, including inadequate consideration of tribal treaty rights and uneven treatment of the project's impacts on native and non-native populations.