Why does the key decision on permitting the Dakota Access oil pipeline rest in the hands of the U.S. Army, an institution whose primary mission does not involve weighing energy policy, environmental consequences or tribal sensitivities?

The question is a crucial one as the Army has granted the pipeline owner Energy Transfer Partners the final easement needed to complete a route that crosses four states, more than 200 waterways and hundreds of wetlands under federal oversight. But while the Army is in charge of issuing that easement, no agency has been in charge of evaluating the entire project.

“Crude oil pipelines like Dakota Access are constructed without any overarching or centralized permitting scheme — relying instead upon piecemeal state-by-state approval, with federal permits required only where the pipeline crosses federal lands, including tribal lands, or federal water,” said Maranda Compton, a lawyer at the firm Van Ness Feldman specializing in natural resource firms and Native American law. “This whole permitting scheme is a real mess.”

The result has been an unusually open display of interdepartmental discord and political intervention from the Obama and Trump administrations. On his fourth full day in office, President Trump ordered the Army Corps of Engineers to cut short a review sought by former president Barack Obama that was impeding the pipeline’s permit.

The Interior Department, Environmental Protection Agency and the Advisory Council on Historic Preservation attempted last year to slow the Army Corps’ decision, writing letters citing the danger of leaks, environmental justice and the lack of public participation.

Like much of American law, the authority over oil pipelines is a patchwork of outdated legislation with the overlay of a newer bill that in turn is the legislative product of congressional bargaining and compromise.

The authority of the Army and the Army Corps dates back to the Rivers and Harbors Act of 1899. The law prohibited the construction of wharves, piers, bulkheads, jetties or other structures in ports, harbors, canals or navigable rivers — except when recommended by the chief of engineers and authorized by the secretary of war.

Later, the Army Corps of Engineers approved the construction of dams and water projects from the upper Missouri River to New Orleans, many of them ill-conceived, harmful to the environment and subject to the pleadings of members of Congress. More recently, it has launched environmental restoration projects in places such as the Florida Everglades.

The Clean Water Act of 1972 reinforced the Army Corps’ authority. It established protections of wetlands and waterways against dredged or filler material from infrastructure projects. Yet it also said that the Army Corps would retain the power to issue permits for projects with “potentially significant impacts.”

That does not mean that the Army Corps considered the entire pipeline project. In fact, no one does that.

Instead, Energy Transfer Partners sought and obtained approval from the public utility commissions in each of the four states the pipeline crosses. It made deals with private landowners for right of way. It went to the Federal Energy Regulatory Commission to discuss rates the pipeline will charge customers.

And it went to the U.S. Fish and Wildlife Service for permits to cross wetlands. In the Dakotas, it crosses hundreds of grassland and wetland areas managed by the agency. In each of the districts, the pipeline required multiple wetland easements and said it would cause “temporary impacts” to 71.8 acres total.

The pipeline’s needs from the Army Corps were limited. It needed easements on waterways under control of the corps. The Clean Water Act said that projects with “only minimal adverse effects,” could obtain a “general permit” issued on a nationwide, regional or state basis. That permit eliminates individual review and allows certain projects to move ahead with little or no delay.

“There wasn’t any meaningful public process,” said Sharon Buccino, a lawyer at the Natural Resources Defense Council, even though the “problems are not de minimus.”

The Army Corps focused on 11 water crossings and asked for more details. It obtained environmental assessments from the company. These assessments are significantly less onerous than the environmental impact statement the State Department required of the Keystone XL pipeline or that the Environmental Protection Agency generally requires from major projects.

Still, they were more than was required for smaller crossings. Moreover, Compton said, “These additional approvals are what triggered the environmental and cultural/historical site review that is at the heart of the dispute.”

Obama stepped in last year, unusual in a commercial dispute such as this one. And he asked Energy Transfer Partners to submit environment impact reports on alternative routes.

Enter the Trump team. In court, lawyers for the government said that Obama’s request for the reports could be withdrawn. On Tuesday, the Army Corps said it would give notice to Congress that it would grant the easement; on Wednesday evening, it did so.

The company issued a brief statement: “With this action, Dakota Access now has received all federal authorizations necessary to proceed expeditiously to complete construction of the pipeline.”