Donald Trump has given every sign that he wants to dismantle the multitude of environmental rules President Obama has put in place over the past eight years. He’s vowed to tear up major climate regulations like the Clean Power Plan. His top pick to lead the Environmental Protection Agency, Oklahoma Attorney General Scott Pruitt, has sued to block nearly every pollution regulation the Obama administration has enacted. Pruitt will no doubt come in looking to make sweeping changes.

That said, it’s not yet clear how far Trump and Pruitt can actually go here. Overhauling the EPA is a surprisingly difficult task that involves navigating a complex bureaucracy bound by powerful laws like the Clean Air Act and Clean Water Act. Ronald Reagan and George W. Bush both came into office hoping to take apart key EPA environmental rules, yet were often stymied by the courts, by green groups skilled at litigation, by career officials, and by sheer inertia.

So what would it actually take for a Trump administration to repeal Obama’s climate and pollution rules?

Jody Freeman, a Harvard law school professor and former climate adviser to Obama, has been looking at this question extensively. Her view is that this won’t actually be easy for Trump — at least not without substantial help from Congress. (Republicans will control Congress next year, and they’d certainly like to dismantle Obama’s climate rules; yet Senate Democrats have also vowed to filibuster any major changes to the Clean Air Act, the source of the EPA’s authority over greenhouse gas emissions.)

I talked with Freeman about the mechanics of a potential Trump administration: how agency rulemaking works, what it would take to revamp Obama’s EPA regulations, why some environmental rules are much more vulnerable than others, and why Trump may not be able to undo everything Obama has done on climate. It’s a little weedy, but these topics are likely to come up again and again in 2017 and beyond. Our conversation has been lightly edited for length and clarity.

Brad Plumer

Okay, say you’re Donald Trump and you enter the White House hoping to undo all the different environmental and climate rules that Obama has put in place since 2008 via the executive branch. What is the first thing you do on day one?

Jody Freeman

So the first thing a new White House would do is essentially issue a stop-work order to the federal agencies — they freeze any pending rules coming out of those agencies and review them. In the past, most of those rules have wound up getting finished, and only very few of them usually get rolled back or reconsidered.

Brad Plumer

That explains why we’ve seen the Obama administration rush to finalize a host of regulations this year, like the EPA’s fuel efficiency standards for trucks, finalized in August. They want to get them done before Trump’s White House can fiddle with them.

Jody Freeman

Right. Now, in Trump’s case, there’s a possibility that Republicans in the House and Senate could use a little-used law called the Congressional Review Act (CRA) to overturn some of these recent Obama regulations. Basically, any rule under Obama that was finished after late May or early June — it depends how they count it — would be potentially subject to disapproval by a simple majority vote [in both the House and Senate]. [Here is a list of Obama rules that would be vulnerable to CRA disapproval, including emissions standards for landfills, rules around offshore drilling, methane standards for oil and gas drilling, and restrictions on migratory bird hunting.]

The question here is how much they want to prioritize this. The new Congress will have to decide what’s most important on their agenda and do some triage. We’ve been hearing a lot about things they want to do on health care, on infrastructure, on tax reform. So the new Congress will have to ask if they really want to spend the first 30, 60, 100 days on Congressional Review Act fights.

Brad Plumer

As I understand it, if Congress disapproves of a regulation under the CRA, not only does it kill the regulation but the agency can’t actually propose a similar regulation anytime in the future, right?

Jody Freeman

That is what the Congressional Review Act says — the agency can’t come back with anything that’s “substantially similar” in the future. But this has actually never been tested, and no court has ever ruled on it. The CRA has only ever been used once [in 2001, to strike down a Clinton labor rule on ergonomics issued in late 2000]. So there’s a real question about whether it’s legally enforceable. Because some existing environmental laws [like the Clean Air Act] may require a certain type of regulation. So what do you do if that law says you have to regulate and the Congressional Review Act says you can’t do it? This could be a really interesting legal question going forward.

Brad Plumer

Let’s go back to the Trump White House and the Trump EPA. Let’s assume they have halted any ongoing work. And now they’re looking at all these rules that Obama has already put in place and finalized — you’ve got everything from rules on mercury pollution that were finished in 2011 to the Clean Power Plan, which is currently being debated in federal courts. Which rules are the most vulnerable?

Jody Freeman

It’s easiest to just not finish rules that haven’t been finished yet. It’s also straightforward to roll back things that aren’t rules — that is, policies that have not gone through the notice-and-comment process. An example would be the suspension of coal leasing [from federal lands] that President Obama put in place. That was done by secretarial order in the Department of the Interior; you wouldn’t have to go through a long process to lift that suspension.

The rules that are harder to rescind and roll back are rules that have already gone through the time-consuming notice-and-comment process and are final and have gone into legal effect already. For example, the rule on mercury pollution, or the cross-state pollution rule. That takes time and effort to rescind, and in some cases industry would have already started to comply. [Note: Many coal plants have already shut down or spent billions installing scrubbers to comply with the 2011 mercury rule.]

The other category here is rules in legal limbo because they have been stayed by the courts. So that includes the Clean Power Plan and the “Waters of the United States” rule [which redefines which rivers, streams, and lakes fall under Clean Water Act protection]. If those rules get struck down in court, the new Department of Justice in the Trump administration could decide not to defend them or to appeal them any further. In that case, it would fall to the interveners — environmental groups or states, which have to be parties to the case — to take up the mantle and appeal.

Brad Plumer

Let’s take the Clean Power Plan, the rule to cut CO2 from power plants, since that’s the centerpiece of Obama’s climate agenda and the rule Donald Trump has focused on. If this rule is upheld by the court, the stay is lifted and it gets implemented. What can the Trump administration actually do to stop it?

Jody Freeman

The new administration could try to go to the DC Circuit Court — which has heard oral arguments on the Clean Power Plan already but not yet decided its fate — and ask the court to do what’s called a “voluntary remand,” sending the rule back to agency. Assuming the courts agreed, which is not guaranteed, then the EPA could try to rescind the rule and replace it with something new.

But the EPA would have to go out for public comment on that — and that usually takes a year or two. The EPA would also have to address the fact that the agency already had decided the Clean Power Plan, so why are they changing their minds now? What is in the record to support that change? They’d have to make an argument for why they’re reconsidering it, and they would have to defend that in court, because any change would get challenged [either by states or by environmental groups].

[The Trump administration] might try to argue that they don’t think they have the authority to regulate greenhouse gases from existing power plants. Or they could argue that even if they do have that authority, they think there’s a better approach to the standard [than the specific regulation Obama’s EPA set up]. They could say they have a narrower approach to setting the standard, and they might get deference from the court. But that would play itself out in years of litigation.

Brad Plumer

Let’s go deeper on this. How do you actually rescind a rule — like the Clean Power Plan or the mercury pollution rule — that’s already been finalized? What is the step-by-step process a Trump EPA has to go through?

Jody Freeman

There’s a Supreme Court case called FCC v. Fox, which basically says that if an agency changes its mind, it has to come back in and defend the new rule the way it would defend the original rule. You have to be able to defend it as non-arbitrary. And in cases where industry is already relying on the first rule, or where there’s a really strong scientific record for the first rule, the burden on the agency is a little tougher for changing its mind. So there is a legal standard here.

But to change a rule, by law, the agency has to do a public comment period — that’s typically something like 60 days, though it can be up to 120 days. Then the agency has to take time to consider and respond to all the public comments on the proposed rule and develop a record that shows they thought carefully about them. If they try to shortchange this process and rush out a brand new rule, it really will not go well for them when they get into court. The procedural checks the agency has to go through are very important, and a court will invalidate a rule that wasn’t done correctly.

The courts will also invalidate a rule change that, in the substance of it, looks arbitrary to them. So as an example, let’s take the endangerment finding, the first big rule that EPA put out in 2009 that said greenhouse gases endanger the public health and welfare. That has a voluminous scientific foundation behind it. The Trump administration couldn’t just come in and say nope, no more endangerment! There’s almost no chance that would be upheld, because you cannot ignore this record.

Brad Plumer

So if they really wanted to overturn the EPA’s authority over greenhouse gases, they’d need Congress to amend the Clean Air Act — to say something like, “Okay, the Clean Air Act no longer applies to greenhouse gases.” And that all depends on whether a bill like that can get through the Senate, past Democrats who might filibuster.

Jody Freeman

Right.

Brad Plumer

So if we’re just talking about what a president can do all by himself, it seems like there are real limits. We saw this during the George W. Bush era — he had a surprising amount of trouble rolling back many of Clinton’s rules.

Jody Freeman

You saw this when the Bush administration tried to roll back the Roadless Rule [a Clinton-era rule prohibiting road construction and timber harvesting on national forest land]. That went through a long, complicated litigation process, and ultimately the new administration wasn’t successful.

The Bush administration also came out and said they would reject the Clinton administration’s arsenic standard for drinking water, and that proved to be a political disaster for them — because, you know, the public doesn’t like to be poisoned. And that was also litigated, and [after eight years] the Bush administration ended up sticking to the Clinton standard.

So those are cautionary tales. We have seen Republican administrations come in before and try to roll things back. And [a Trump administration] may well be successful on some of these high-profile rules, but it’s going to be trench warfare. They’ll have to pick their battles.

Brad Plumer

So what’s the lowest-hanging fruit for a Trump administration? Where will they have the easiest time prevailing?

Jody Freeman

Well, the Clean Power Plan isn’t low-hanging — it will take a lot of work to change. But because Trump has identified it on the campaign trail, and it’s in the sights of many Republicans in Congress, it’s hard to imagine they won’t take action of some type. There’s also quite a bit of congressional hostility to the Waters of the United States rule, so you’ll likely see something there.

There are easier things to do — like if the Obama administration finishes the stream protection rule [an Interior Department rule that governs mining waste disposal in waterways], you could imagine a Trump administration trying to roll that back before it becomes legally effective. And like I said, the coal leasing moratorium can be lifted with a stroke of a pen.

Brad Plumer

And of course, Trump can withdraw from the Paris climate agreement unilaterally. I’ve seen a few different ways he might do this — like withdrawing from the 1992 UN Framework Convention on Climate Change, the original treaty establishing international climate talks that undergirds the Paris accord. Which seems most likely?

Jody Freeman

It is possible to withdraw from the framework convention — that’s actually faster than withdrawing from the Paris agreement, since Paris takes four years to officially withdraw, whereas withdrawing from the UNFCCC takes one year.

The problem is that the UNFCCC was a treaty unanimously ratified by Congress [in 1992], there was no real dissent, and it was negotiated by a Republican president. The UNFCCC also has no real substantive obligations in it. So it would be a very odd thing to withdraw from — it would do a lot of damage, upset our allies enormously, and you really don’t need to do it [if you’re trying to undermine the Paris deal].

What Trump could much more easily do is simply not meet the US pledge for Paris. Or he can just say, “I’m not going to be bound by that pledge, and I’m going to take apart the key programs domestically that were supposed to get us there, like the Clean Power Plan.”

Brad Plumer

Tell me about the Office of Information and Regulatory Affairs (OIRA), which is part of the Office of Management and Budget. It seems like this will really change under Trump — with potentially major implications for regulatory agencies like the EPA.

Jody Freeman

OIRA is the location in the White House where they oversee agency rulemaking. This office oversees the methodology that agencies use to count up costs and benefits for new rules. That can be changed with the stroke of a pen. And it sounds weedy, but it’s the kind of thing that can make it harder to issue new regulations.

So for instance, right now the Obama administration currently uses a “global social cost of carbon” for its climate rules — that means if you have any rule that reduces greenhouse gases, the benefits counted for that rule include the [climate] benefits globally. You could imagine a Trump OIRA saying, “We don’t want to do that anymore. We’re not going to count the social cost of carbon as a benefit.” That changes the calculus for which rules are cost-beneficial.

OIRA is also the place where, if the Trump administration were serious about their idea of trying to repeal or rescind two rules for every new one they issue, that’s where they’d do it — though it’s hard to imagine how [this idea] would possibly work.

Brad Plumer

There are also a whole bunch of executive orders that were issued from the Obama White House, not the agencies themselves. Like this 2013 order that told the agencies to help communities prepare for climate change. Those executive orders can be easily reversed, right?

Jody Freeman

That’s right. That also includes guidance from the Council on Environmental Quality that governs how agencies should consider greenhouse gas emissions when they conduct environmental impact statements. Every agency has to do these environmental impact statements [for instance, the State Department had to do one before approving the Keystone XL pipeline]. So [the new Trump White House] could say, “We don’t want you to consider GHGs anymore.”

That’s stroke-of-a-pen stuff. Every executive order can be replaced with a new executive order, or withdrawn completely. And there’s nothing that the environmental community or the states can do to challenge executive orders directly. Although there’s a twist here: When the executive orders tell agencies to do things, and then the agencies do those things, that’s when they get legally challenged.

Brad Plumer

A slightly different question. Even if the Trump administration has a hard time rescinding specific Obama-era environmental rules, can’t they still weaken enforcement of these rules?

Jody Freeman

There are a lot of ways to slow down implementation and to try to minimize enforcement. Everyone talks about the Reagan administration as a good example of the EPA being “dismantled from within” — by slow-walking regulations, by slow-walking enforcement.

That said, there are a lot of internal checks on this kind of dismantling from within. There’s a very dedicated career staff that knows it has to follow the law, and there are ethics rules that apply to the agencies; there are independent inspectors general that are tasked with making sure there’s not mismanagement or ethics violations. So not only will there be lawsuits from outside when agencies don’t follow the law but there are management rules and procedures inside that should create some obstacles to any real effort to undo them.

That said, a very determined administration that really wants to pull back on implementation and enforcement will find ways to pull back. They can give more leeway to the states, for example, when the states draft their plans for complying with their state implementation plans [for EPA pollution rules like the ground-level ozone standard]. You can imagine ways of making it easier for states that don’t want to work very hard. Or bringing fewer enforcement actions.

The president can also ask for less money. And even if he doesn’t, Congress can just cut the budget [for agencies like the EPA]. Congress can insert, in big omnibus budget bills, little riders that say agencies can’t do specific things. There can be death by a thousand cuts in this way.

So I don’t want to suggest there won’t be retrenchment. But what some people fear is that Trump is sworn into office and he eliminates the EPA. That just can’t happen; he’d need Congress to do it, and I don’t think that kind of dramatic action is anything we’re going to see.

Brad Plumer

Right, it’s hard for Congress to simply abolish the EPA or rewrite the Clean Air Act — that would face a potential filibuster. But it’s far more plausible that we might see the House pass a thousand different riders that change the agency significantly. The GOP House has been trying to pass a bunch of these since 2011.

Jody Freeman

I think it’s realistic to think there will be some of that. We have seen the House try to pass lots of things, though of course that was when they knew they couldn’t succeed. Then again, when you control both houses of Congress and you’ve got the presidency, you have to watch what you do. Because dismantling the nation’s environmental laws is not going to go over well with the public.

Brad Plumer

Trump hasn’t yet said who he would appoint to run any of the key environmental agencies, but what are the things to watch for here? How much leeway does the individual at the head of an agency have to change things?

Jody Freeman

Well, if we see appointees to the EPA and Department of the Interior and Department of Energy, all of whom have disdain for environmental protection, this would be a real potential problem, because it would mean the political appointees at the top are opposed to these agencies’ essential missions. That obviously has an impact on career staff, on the morale.

But at bottom, you have to remember that these agencies are creatures of law, they are tasked with implementing statutes, and they can’t not do it without being threatened by litigation saying they are behaving unlawfully. So even political appointees will be disciplined by legal requirements.

There’s another effect that also happens — and I’m not saying this always happens — but it’s quite standard for political appointees to come in and then be exposed to the mission of the agency, and have senior staff brief them, to learn something about the agency and enlarge their perspective. And they end up moderating some of their views.

Brad Plumer

There’s another side of this, too. The Trump administration isn’t just going to be focused on overturning Obama regulations. There are also laws that were passed by Congress like the Clean Air Act that will continue to require updates of existing regulations over time, on a set schedule. How much can appointees that are philosophically opposed to regulation really drag their heels here?

Jody Freeman

There is some leeway for agencies to miss deadlines; they miss deadlines all the time. And courts don’t strictly enforce every deadline if the agency can show it’s making reasonable progress. At some point, though, courts will step in and require agencies to take some action.

But you’re asking will there be some slippage? Certainly there will be some slippage. Agencies can miss deadlines by a year, two years, and courts will give them a lot of room, because they recognize agencies have a lot of priorities. But if an agency routinely and systematically misses deadlines and it looks like political interference, then courts may become quite skeptical.

What’s interesting is that even courts that are viewed as conservative and have a lot of conservative appointees, they respect the rule of law. And they may well wind up providing an accountability mechanism for any real effort to stymie these agencies systematically.

Brad Plumer

Okay, but what if Trump starts filling the courts with appointees more likely to rule in his favor?

Jody Freeman

Yeah, you may get judges who are more skeptical of ambitious regulations — or regulations that creatively press the boundaries of a statute. But for run-of-the-mill rules and deadlines, it’s just a sort of lawyerly disposition to respect the rule of law. It’s hard to find judges that will systematically turn a blind eye to the core demands of the agency’s mission. There will be some brakes on what they can do.

I realize I sound almost cheerful — I am not! I’m not saying there’s no problem here.

Brad Plumer

It does sound like the main point here is that the federal government is this vast bureaucracy that can’t just be turned around overnight.

Jody Freeman

Yes, that’s exactly it.