Donald Trump has long talked about reining in the Environmental Protection Agency (EPA), which is in charge of enforcing federal laws on air and water pollution. It’s a top priority for his supporters in the fossil-fuel industry.

But there’s still a lot of uncertainty over what, exactly, this will look like. Trump himself has been all over the map on the agency’s future. In Congress, there are bills floating around that would do everything from abolish the EPA to merely curb its powers at the margins. And, while Trump’s pick to lead the EPA, Scott Pruitt, was an ardent foe of Obama’s environmental policies, he’ll face serious legal hurdles in trying to dismantle them all at once.

So, to simplify things a bit, here are five possible futures for the EPA under Trump, based on what we know so far. As noted, some of these scenarios are way more plausible than others — and they’re not all mutually exclusive. But it’s a way of seeing the options here:

1) The EPA gets abolished altogether

This is the least likely scenario by far, though various politicians have brought it up. At one point during the campaign, Trump expressed interest in eliminating the EPA entirely, though he later backpedaled. And in the House, freshman Rep. Matt Gaetz (R-FL) introduced a bill on February 3 to “terminate” the agency — which has an annual budget of $8 billion and employs more than 15,000 people.

But few of Gaetz’s colleagues are taking his bill seriously, and for good reason. Congress can’t just terminate the EPA with one sentence, as Gaetz’s bill does, and call it a day. There are dozens of sweeping environmental laws that have been enacted since 1970 — including the Clean Air Act and the Clean Water Act — that require the federal government to limit air and water pollution. Those don’t disappear just because everyone at the EPA has been laid off. Congress would either have to give some other agency all of EPA’s responsibilities or rewrite America’s bedrock environmental laws. Otherwise, those same laws would leave companies vulnerable to a blizzard of citizen lawsuits. It’d be a nightmare.

Plausibility: This one’s almost certainly not happening.

2) Congress says the EPA can no longer address climate change

In 2007, the Supreme Court ruled the EPA had the authority to regulate greenhouse gases under the Clean Air Act if it determined they pose a threat to public health or welfare. Under Obama, the EPA determined that they do indeed pose a threat, and went about enacting a flurry of climate policies: stricter fuel-economy standards for cars and trucks; limits on CO2 from new and existing power plants; regulations on methane leaks from oil and gas drilling. Those policies help underpin international efforts to tackle global warming.

Trump wants to dismantle these policies. And as head of EPA, Pruitt would have some leeway to scale back rules like the Clean Power Plan for power plants. But so long as the Supreme Court’s ruling stands, Pruitt would still be obligated to enforce some regulation of greenhouse gases (as he has acknowledged). What’s more, so long as EPA keeps its authority, a new president could come in after Trump and pursue more ambitious Obama-style climate policies.

Unless Congress steps in, that is. In the House, 110 Republicans have signed onto a bill, HR 637, that would strip the EPA of all authority over greenhouse gases forever and ever. If it passed, then nearly every Obama-era climate policy would vanish instantly. No more Clean Power Plan. No more carbon standards for new coal plants. No more methane standards. (Fuel-economy standards for cars would be a trickier case.) And no future president could tackle climate change through the EPA.

Plausibility: Low-ish. So far, none of the relevant House committees have taken up HR 637. Senate Democrats would almost certainly filibuster such a bill, and they have the votes to do so — at least for the next two years. And as long as Pruitt is slow-walking the EPA’s greenhouse-gas rules, there’s less urgency for opponents of climate action to pass this. Still, this idea has major support in the GOP caucus, and it’s likely to come up again and again, especially if Republicans pick up seats in the midterms.

By the way, it’s unlikely that Pruitt can tear up the EPA’s Endangerment Finding, the 2009 analysis establishing that greenhouse gases were a threat and therefore need to be regulated, without Congress. “That has a voluminous scientific foundation behind it,” said Jody Freeman, a Harvard law professor and former Obama climate advisor. “The Trump administration couldn’t just come in and say nope, no more endangerment! There’s almost no chance that would be upheld [in court].” Plus, in a weird twist, if the EPA’s authority were repealed, that could open the door for common law suits against polluters in the states — a potential nightmare for companies.

3) Scott Pruitt tears up Obama’s environmental policies

If Congress doesn’t make fundamental changes to the way the EPA does business, then it will fall to Pruitt and his team to reshape the agency. As Attorney General of Oklahoma, Pruitt teamed up with oil and coal companies to challenge much of what Obama’s EPA did on environmental protection. While he usually lost those fights in court, he’ll now be in a better position to roll back many of EPA’s rules.

Pruitt has to work within the confines of the Clean Air Act. But he could, for instance, begin the multi-year process of rewriting the Clean Power Plan, which regulates CO2 from power plants. Whereas Obama’s rule would prod states to shift to cleaner energy and slash emissions 30 percent below 2005 levels by 2030, Pruitt’s EPA could craft a more modest version that merely pushes coal-plant operators to improve their heat-rate efficiency. That might lead to a smaller 2 to 4 percent cut in emissions — and would be a significant setback for US climate action.

Similarly, Obama’s EPA crafted a rule that made it impossible for new coal plants to obtain permits unless they could capture and bury their CO2 emissions underground. A Pruitt version might merely require new coal plants to be ultra-efficient. He could also try to rewrite the EPA’s “Waters of the US” rule so that the Clean Water Act applied to fewer streams and wetlands. He could tweak the EPA’s fuel-economy standards for cars and trucks so that they were less stringent. “There’s limited bandwidth here,” says Jeffrey Holmstead, a top EPA official in the George W. Bush administration. “But if I had to guess, I’d guess they get a couple of these big changes done.”

On top of that, although EPA is eventually supposed to regulate other sources of greenhouse-gas emissions, like refineries and chemical plants, Pruitt could delay the introduction of these rules indefinitely. Pruitt could also stock the EPA’s scientific advisory board with more industry-friendly appointees, which could lead to less-aggressive environmental rules overall. And he could explore ways to weaken the agency’s enforcement capabilities, as he did in Oklahoma.

Plausibility: High. Although he doesn’t have unlimited power here, Pruitt would be in a good position to significantly weaken US climate policy — and make it very difficult for the country to fulfill its climate pledge under the Paris deal. The one wild card is that EPA regulatory changes have to go through a laborious rule-making process and can be challenged in court by green groups. Pruitt may lose some of those battles, though it’ll be tougher to challenge him on things like delaying new climate rules.

4) Pruitt and Congress handcuff the EPA through budget cuts

Rewriting regulations isn’t the only way for the Trump administration to curtail the EPA. They’ll also submit budget requests to Republicans in Congress, many of whom want to shrink the agency considerably.

Last year, Rep. Ken Calvert (R-CA), who chairs the House committee overseeing the EPA’s budget, pushed a budget proposal that would freeze EPA staffing levels at 15,000 positions and cut the agency’s enforcement capabilities by about 6 percent. But other Republicans in the House want to go much, much further, cutting the agency’s budget as much as 30 percent. And Myron Ebell, who led Trump’s EPA transition team, has suggested cutting 10,000 of the agency’s 15,000 positions.

On top of that, in the past, Republicans have pushed to add dozens of anti-EPA riders to budget bills that would impose various restrictions on the agency. That included riders barring the EPA from researching the environmental impacts of fracking. Riders stopping the EPA from enforcing pollution from livestock production. Riders preventing the EPA from enforcing lead-paint exposure rules. Riders to block certain greenhouse-gas reporting requirements. And on and on. The Obama White House typically opposed these. The Trump White House may be more receptive.

Plausibility: Medium to high. While it’s less likely that Ebell’s grand ambitions to gut the EPA’s workforce will come to fruition — he no longer has much influence with the White House — Congress is very likely to chip away at the EPA’s budget and add various riders to curtail the agency’s regulatory authority. Industry groups will be lobbying for these constantly, and environmentalists may struggle to play defense here.

5) The EPA survives the Trump years (mostly) intact

After years of Trump, it’s quite possible the EPA will find itself radically transformed. Congress rewrites the laws guiding US environmental policy — or at least chips away at them through budget riders. Pruitt dismantles Obama’s climate rules. Budget cuts and layoffs do lasting damage to the agency’s regulatory capacity. Enforcement is pared back drastically or handed over to the states, and industry enjoys far looser oversight. US greenhouse-gas emissions are much higher than they would’ve been otherwise.

But that’s not inevitable. It’s also possible that Congress will be unable to strip the EPA of its greenhouse-gas authority or to pass bills like the REINS Act that would drastically restrain new agency rule-making. It’s possible that Pruitt’s efforts to reshape Obama’s EPA rules could get bogged down by lawsuits from opponents, and he finds himself unable to change all that much. It’s even conceivable that the EPA could emerge from the Trump era in roughly the same shape it’s in today — albeit having made little progress on climate change in the interim.

Plausibility: Who knows? Both Ronald Reagan and George W. Bush tried to downsize the EPA, attempting to hack away at regulations and make life easier for industry. Both made some headway in weakening environmental protection — but at the same time, many of their more brazen efforts got beaten back in court. (See, for instance, Bush’s failed attempts to issue weaker standards on smog.) During the Bush years, states sued the EPA and got the Supreme Court to order the agency to deal with greenhouse gases. By 2009, the US had lost time in tackling carbon emissions, but Obama was able to reorient the agency in just a few years.

That said, Bush’s team was never as outwardly hostile toward the EPA’s mission as Trump’s has been. And there are so many variables here: How active will Congress be on legislation? How savvy will Pruitt’s team be about crafting legally defensible EPA rules? How will federal judges swing? Will the agency’s career staffers resist drastic changes in policy? It’s going to be an unpredictable four-plus years.

Further reading