With the election of Donald Trump, environmentalists find themselves bracing for their worst possible scenario at the worst possible time.

Only recently, the world has made slow but steady progress in the fight against climate change — even as signs of global climate disruption have accelerated. The world has already warmed about 1 degree C above preindustrial times, which might not sound like much, but scientific evidence shows it’s contributing to an increase in extreme weather, drought, and conflict across the globe. If we don’t ramp up immediate action to limit warming, the consequences will become more deadly, even catastrophic, for the world’s most vulnerable populations.

History could one day judge this election as the point of no return. Our science-adverse, climate-denying, fossil fuel–friendly president-elect promises to take a wrecking ball to the few promising signs that the world is beginning to deliver on a more sustainable future.

At best, it will turn out that Trump (never one for consistency) was bluffing during his campaign. Republicans could still decide not to fulfill their promises to cut all federal climate funding and cripple the Environmental Protection Agency. Perhaps the international backlash can slow Trump’s roll to pull the United States from the Paris climate deal.

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But at worst — and this is the way things appear to be leaning — Trump and his administration of fossil fuel executives will undo not just the incremental progress made under President Obama’s second term, but over 40 years of environmental progress since the inception of the Clean Air Act. Millions, even billions, of people could be hurt because of a single U.S. election, especially if America’s reversal sabotages the climate efforts of other countries.

Facts and science have often taken a beating in U.S. politics, and advocates will find themselves in a familiar, if daunting, position over the next four years: limiting what the presidency can do to unwind climate action.

Progressives across the board are now navigating a post-election minefield. Some have been tempted to normalize Trump’s positions and pledge to work with him if he comes around, while many others have no illusions about what his presidency will bring. In wide-ranging interviews across the movement in the week after Trump’s election, environmental leaders and activists explained how they are gearing up to fight.

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Their message: Have hope.

Strategy 1: Apply public pressure

At a sober press conference the day after the election, Kevin Curtis, president of the Natural Resources Defense Council Action Fund (the political affiliate of the larger national group), made a weak joke about how many of his fellow speakers had gray hair. His point: Many of them have faced these battles before, specifically when Republicans controlled Congress in 1980, 1994, and 2004, and promised to handicap the Environmental Protection Agency, just as Trump has.

“The environmental community experienced this 16 years ago with President George W. Bush,” echoed Erich Pica, president of Friends of the Earth, in a separate interview. “We used the courts to protect rules. We went after political appointees, personnel policy.”

Each time a Republican president took office over the past few decades, environmentalists saw protections and oversight rolled back or delayed, resulting in loose standards for air pollutants and loopholes in fracking regulations. We’re still seeing ramifications of those changes today.

But advocates also successfully fought many proposals that could have permanently handicapped the Clean Air Act and environmental enforcement.

“When Newt Gingrich came in, as the public realized what he was actually intending to do, the public became very active in voicing concern, as did media and others,” said David Goldston, NRDC’s government affairs director. “There was a level of attention and criticism that made Gingrich and his allies realize they were expending too much political capital on an anti-environmental agenda that was not successful.”

Another such fight involved Bush’s Energy Policy Act of 2005. Now infamous for the “Halliburton loophole” that prevents federal oversight of hydraulic fracturing, environmentalists who were fighting many of the act’s provisions at the time remember it for its potential to do far worse.

“It was a laundry list for polluters, and really nothing that was going to benefit America and move us toward a clean energy future,” Environment America’s D.C. Director Anna Aurilio said. “We fought hard against that bill for five years.”

Filibustering blocked, among other things, the opening of the Arctic National Wildlife Refuge, and kept many public lands off limits to drilling. Environmentalists mobilized their supporters to call on Senate leaders to block the worst of the fossil fuel wishlist.

Another tactic that seemed to work, Friends of the Earth’s Pica noted, was exposing the many ties between the fossil fuel industry and the Cheney energy task force that recommended changes in the law and regulations.

The parallels between the second Bush administration and today aren’t exact. The GOP held less extreme positions on climate change than it does today, and even then enviros lost on many fronts. It is unclear whether Democrats will even have the filibuster, which allows the minority party in the Senate to block legislation, at their disposal this time around.

There are other differences that offer a bit of hope, though. “The stakes on climate are far higher, and this time the urgency is greater,” NRDC’s Goldston said. “I think the prominence of where the issue starts is more prominent than where pollution was when the Reagan, Bush, and Gingrich fights took place.”

Strategy 2: Thanks, Obama

Obama’s lame-duck period won’t be boring, that’s for sure. Before the president leaves office in January, enviros expect their most powerful current ally to push through a series of finalized regulations and public-lands protections, setting up obstacles to a Republican polluter-free-for-all.

Activists are pressuring the administration to deny the permits that would allow completion of the final leg of the Dakota Access Pipeline under the Missouri River. They are pressuring Obama to take the Atlantic coast and Arctic Ocean off the table in his five-year drilling plan. (Less realistically, they hope to see the Gulf off-limits for more drilling, too).

There’s also a push to declare the area around the Grand Canyon off-limits to uranium mining. And enviros are asking Obama’s EPA to finalize as many anti-pollution regulations as possible.

The problem is that whatever Obama can do by executive action can be undone just as easily by executive action, or by Congress. Republicans are already eyeing reigning in one of the presidency’s greatest environmental powers of the last century — the ability to designate national monuments. Even if Obama fulfills every last item on environmentalists’ wish list, it doesn’t mean his actions will withstand the test of time.

That’s not the point, argues one of the groups pushing the administration to do more.

“Even if these things are busted up after the Obama administration,” said 350.org Communications Director Jamie Henn, “at least it forces Trump to actively break them, instead of letting him charge ahead.”

Strategy 3: Sue the bastards

Environmental groups weren’t ready to comment in detail about their legal strategy in a Trump era. They already have their hands full with the legal defense of the Clean Power Plan (Obama’s regulations to reduce carbon emissions from power plants) and other Obama-era regulatory cases that are threading through the courts.

They have the law — at least for now — on their side. The Supreme Court has upheld the EPA’s ability to regulate pollution, and has also determined that, technically, the government must address greenhouse gases, if the best science says they’re a threat to public health (they are).

Under Obama, the EPA already issued these so-called endangerment findings, confirming the science underpinning the health threats of climate change, and a president can’t simply reverse those with the stroke of a pen.

Environmental groups could be expected to go on the offense and not just play defense, maintaining that — by law — the government has to address climate change.

Although court battles sometimes work, they can’t perform magic. A Trump administration will still be governed by anti-science personnel and strategy, and one of the easiest solutions from them to stall environmental action would be to cut funding to agencies’ most important work. Lawsuits are also contingent on judges who go by precedent and rule for the environmental side, while many lower courts are staffed by more conservative justices.

“Legal strategies are end-of-the-pipe solutions,” activist and Environment Action policy director Anthony Rogers-Wright said — meaning they are the last line of defense.

Strategy 4: Win in the states

Much of the progress on climate change over the past decade has occurred at the state and local level, and that will be even more true in a Trump era.

Large environmental and progressive groups have reported record fundraising in the days after the election. Community-based groups have also seen an outpouring of support.

Elizabeth Yeampierre, who runs UPROSE, a group focused on environmental justice in Brooklyn, said that this week alone she has seen a flood of interest from community members interested in volunteering. “It took us by surprise,” she said. “People are looking for community anchors, spaces they can organize, spaces they can preserve our rights, and move the dial forward on climate change.”

“What I find most promising and most exciting is the level of concern and interest in supporting organizations like ours.” One of UPROSE’s main focuses in the upcoming year will be turning the industrial waterfront off Brooklyn’s Sunset Park into a hub for sustainable development and offshore wind.

“It’s interesting,” Yeampierre said. “People say that’s very local, very parochial, but areas like those are well-positioned to serve regional and local needs at the same time.” It’s those kinds of efforts in which progress on sustainability could continue during the Trump years.

Bold Nebraska’s Jane Kleeb, for her part, is ready to organize against a renewed push to approve the Keystone XL pipeline. (Builder TransCanada has already announced plans to reapply for a permit under the Trump administration.)

“We will start to really hit Republicans on the eminent domain issue,” Kleeb said. Forcing landowners to turn over their property for pipelines, which allows private companies to profit, is unpopular with both Democrats and Republicans.

“We’ll continue to fight pipelines around property rights, water, and sovereignty issues,” Kleeb added. “We’ll be fighting for public lands and water.”

Whether it’s blocking a coal-export terminal in Seattle or California passing ambitious climate legislation, those local fights will grow even more important as Trump tries to move the country in the opposite direction.

Republicans will have the least control over trends in state and local clean energy development, which have been dictated more by economic factors than political ones. Of course federal policy still helps shape those trends, especially in the remote possibility that Congress zaps clean-energy tax breaks.

Nevertheless, for at least the next four years, progressive states will continue to take the lead in climate policy in the United States. While some states get cleaner, Republican-dominated states could very well go in the opposite direction as the federal government lowers the bar they’re required to meet.

Strategy 5: Expand the movement

The climate movement has a tool at its disposal that no election can take away — the movement itself, which has changed dramatically over the past few years and now includes a much larger coalition of faces and groups.

That new mix was on display two years ago at the 311,000-strong People’s Climate March in New York City, as frontline communities and environmental justice advocates led the way.

Advocates agreed that to succeed, environmentalists are going to have to lean even harder into a broad-based strategy that engages more people and new allies in the climate fight.

Yong Jung Cho, a former organizer with 350.org who is a cofounder of the new progressive group All Of Us, notes that although single-issue organizing is important, “we need movements” that push a broader set of priorities from the outside.

All Of Us will be less concerned with organizing against the GOP’s racist agenda than with pressuring Democratic politicians to hold the line, Cho said. This week, the group organized a sit-in at the office of Sen. Chuck Schumer, expected to be the next Senate Minority Leader.

To organize effectively in a Trump era, Rogers-Wright said “our local organizing prowess is going to have to improve and increase tenfold. We’ve seen some amazing things happen at the local level that have had a lot of profound change.”

Just look at the rallies across the country this week calling on Obama to do whatever he can to permanently stop construction of the Dakota Access Pipeline in North Dakota before he leaves office. What began as a legal battle between the Standing Rock Sioux Tribe and the pipeline owner, Energy Transfer Partners, has become a national rallying cry for indigenous rights and protecting clean water, resonating as few environmental battles have in recent years. Tens of thousands of people have now taken action in solidarity with what began as a local fight.

Similarly, Sierra Club Executive Director Michael Brune says he finds hope in the growth of a different kind of coalition that has emerged as clean energy has become competitive economically.

“When it comes to climate and clean energy, there is an alliance between the market and our movement that we never had before,” Brune said. “Clean energy now is cheaper than coal and gas in most parts of the country, and it creates more jobs than fossil fuels. Investors are increasingly moving away at least from coal — investors and corporate leaders that we didn’t have in the Bush administration.”

Whereas a strong progressive movement would apply pressure to Democrats and more moderate Republicans, business leaders might carry a bit more weight among conservatives. The pressure has already started, as more than 360 businesses have called on Trump to stick with the Paris climate deal.

At first glance, these two goals — shoring up a wider progressive base of climate voters and appealing to business interests — might seem in conflict. But that’s not necessarily true.

“The way that movements work and are most effective is not that everyone does the same thing, or that everyone adopts the same messaging,” said 350.org’s Henn. “It’s about having a diversity of approaches that work together — an ecosystem, if you will — that are somewhat in concert with one another.”

Key to this strategy, Henn said, is not forgetting the larger stakes of the fight.

“It’s important to remind people that that there’s something fundamentally awful about what he’s doing. It’s going to be important to not normalize the Trump agenda. … The climate community is going to need to keep doing that. If we fight this as a policy fight, we’re going to lose.”