If you ask US climate activists which federal agency will be most essential in any future effort to enact a Green New Deal, you’ll often get the same response: the Environmental Protection Agency, of course. You know, the agency with 14,000 employees, which regulates power plants and was responsible for crafting President Obama’s Clean Power Plan. The one with that sexy superhero name and plenty of mainstream press coverage. It’s a solid commonsense answer—and also a mistake.

“When people say it’s the EPA, I’m like, ‘What are you talking about?’” says Nada Culver, a former senior attorney at the Wilderness Society and now a vice president at the Audubon Society. “Do you know which agency is doing all the leasing and permitting? Do you know which agency is leasing out all our public lands to oil and gas companies while completely ignoring climate change?”

While no one doubts the EPA will play an enormous role in the fight to confront the fossil fuel cartel and abate the climate crisis, Culver and other longtime climate advocates have their eyes on a much larger bureaucratic behemoth: the US Department of the Interior (DOI).

Despite its bland name and relatively low profile, the Interior Department’s influence on this country’s response to the climate crisis is almost impossible to overstate. The largest environmental regulator in the land, the DOI boasts about 70,000 employees, including some 10,000 scientists, making it more than four times the size of the EPA.

This mammoth institution administers roughly 500 million acres of federal land across the nation, or one-fifth of the United States’ landmass. It manages vast tracts of oil, gas, coal and other mineral resources, including the entire outer continental shelf. It is the chief regulator of coal mining in America, even on private lands. It oversees the Bureau of Indian Affairs and the Bureau of Reclamation, the American West’s principal dam-building agency. It runs the National Park Service and controls more than 500 wildlife refuges nationwide. And it enforces the Endangered Species Act, perhaps our most powerful environmental law.

What’s more, roughly a quarter of all greenhouse gas emissions in the United States derive from fossil fuels drilled and mined on land that the agency controls. Despite a perennial dearth of coverage in big-name news outlets, the Department of the Interior is the place where an enormous portion of the Green New Deal will likely take shape.

“The Interior Department has to be front and center on this,” says John Ruple, a professor of law at the University of Utah who specializes in public land policy. “They control the land where the future happens—whether we are talking about renewable energy development or a new Civilian Conservation Corps—and they control the land of the past,” which is to say, the millions of public acres scattered with oil and gas rigs, coal mines, pipelines, and more.

In other words, the path toward environmental healing in the United States passes through the Interior Department. That’s where critical Green New Deal policies will be translated into reality. It’s where plans to ban offshore and onshore drilling will largely take shape. It’s where Bernie Sanders’s plan to invest “$171 billion in reauthorizing and expanding” the Civilian Conservation Corps will get hammered out. And it’s where Elizabeth Warren’s proposal to develop offshore wind projects from Maryland to Maine will evolve from theory to practice.

The problem is, none of it will be easy. Even if an eager, committed president takes office in 2020, the job of turning the DOI into a vanguard force in the fight to stanch the climate crisis will be a formidable challenge—thanks, in no small part, to the work of the Trump administration.

For the last three years, the Trump team has been busy turning the Interior Department into the equivalent of an ecological suicide vest. It has used the agency’s vast powers to erode environmental laws, purge knowledgeable civil servants, monkey wrench regulations, and lock in fossil fuel production on federal lands for many years to come. At this very moment, there are roughly 24,000 oil and gas leases on federal land in production. More than 450,000 federal acres, meanwhile, are leased out to coal mining concerns.

And that’s really just the beginning. From the Arctic National Wildlife Refuge in Alaska to the Boundary Waters Wilderness in Minnesota to the Bears Ears region in southern Utah, the administration has attacked protected lands from coast to coast in an attempt to open them up to the extractive industries. In fact, President Trump’s destruction of the Bears Ears National Monument in Utah in December 2017 amounted to the largest single rollback of public land protections in American history—and all for the benefit of right-wing pressure groups, ranching interests, and mining firms.

“They have essentially gutted the agency,” says Representative Deb Haaland of New Mexico, a key leader on public lands issues in Congress.

To erase Trump’s legacy at Interior will require years of strategic effort. Among other things, an incoming progressive administration will have to rebuild the DOI’s civil service, which has been badly damaged by the Trump team’s drive to push out competent personnel, especially at the crucial Bureau of Land Management. It will also have to undo Trump-era rules, regulations, and proclamations that have eviscerated key laws like the Endangered Species Act, the National Environmental Policy Act, the Antiquities Act, and the Migratory Bird Treaty Act. It will have to reverse secretarial orders that direct the department to fast-track fossil fuel development on federal land. And it will have to review and revise a slew of land management plans that have provided free rein to oil and gas drillers, mining interests, and more on the public domain.

All of the above will take an enormous amount of time and talent. And that’s just defense, a rear-guard action to limit the damage inflicted by a previous administration. To regroup and go on the offense will be another challenge entirely. How, for example, will a future administration actually “end all new and existing fossil fuel extraction on public lands”—a key plank of Sanders’s plan for a Green New Deal? Will Sanders simply kick these oil and gas rigs off the land? Is that even possible?

Assuming that a pro–Green New Deal administration doesn’t come into office with an enlightened Congress ready to legislate the climate movement’s priorities, it will have to use executive authority to achieve its goals. As it happens, using such authority to immediately end new federal land leasing at least seems possible within the confines of existing law. Under the Mineral Leasing Act of 1920, the secretary of the Interior has the discretion to halt new federal land fossil fuel leases, says John Leshy, a law professor at the University of California Hastings and the Interior Department’s top lawyer during the Clinton administration.

“A nearly complete moratorium [on new federal land fossil fuel leasing] is actually pretty feasible legally,” says Leshy. “You can do it. And politically, it is not totally unrealistic either.”

On the other hand, immediately ending existing fossil fuel extraction on federal lands is an entirely different matter. Leshy calls it “pie in the sky.” The oil and gas leases that are in effect today—and again there are tens of thousands of them—are the subject of legally binding contracts between the federal government and private oil and gas firms. Unless Congress is prepared to appropriate hundreds of millions of dollars or more to buy out these contracts, proponents of the Green New Deal will almost certainly have to find other ways to crack down on current oil, gas, and coal operations on federal lands.

“As of last count we have about 26 million acres of federal land under lease,” says Culver of the Audubon Society, who is an expert on federal land energy development. “It’s not necessarily impossible, but it would be a significant undertaking to figure out how to stop development universally on existing leases.”

Moreover, the fossil fuel industry won’t be the only force the DOI will have to contend with. State budgets in places like New Mexico and Wyoming are hugely dependent on fossil fuel revenues from public lands. A just transition in such states will require highly competent federal leadership capable of developing large-scale renewable-energy generation and transmission projects along with other economic programs. The same goes for the creation of jobs programs like a new CCC, which will also need a massive, well-planned mobilization at the DOI.

What this means in practice is that any future administration that seeks to aggressively combat the climate crisis while creating millions of good jobs will have to come into office on day one with an incredibly detailed plan for the Interior Department. It will need an all-star team of lawyers, planners, administrators, and scientists who know exactly what they are doing. And it will need a movement behind it that truly understands the importance of this agency, an agency too often ignored, even by climate activists.

It’s time to start paying attention to the Interior Department.