In a roomful of oil and gas executives in North Dakota late last month, Donald Trump reiterated his threat to “cancel” the Paris climate agreement, insisting the way to “make America great again” is to resurrect the coal industry and drill our way to prosperity.

But even if Trump is elected, taking down Paris is going to be a lot harder than he thinks. That’s certainly the view of Jonathan Pershing, President Obama’s new climate envoy, who’s rushing to Trump-proof America’s commitment to the pact—minimizing ways in which a President Trump could obstruct the global carbon reduction plan.

“We’re all in. We’re moving down this road,” says Pershing, who is seated on a couch in his office at the State Department, surrounded by relics of past climate negotiations. Pershing picks one up—the original United Nations document that launched them, back in 1990—as if to emphasize just how long people like him have been working to save the planet before Trump came along. The veteran diplomat, a distant relative of Gen. John "Black Jack" Pershing of World War I fame, has been in the room for many of these talks and it’s clearly a point of pride with him. Pershing took the mantle from Todd Stern in early April and is now part of a small team of senior administration officials who are trying to cement durable regulations on climate that will survive after Obama leaves office, no matter who succeeds him.

Pershing is now trying to lock in the U.S. side of the accord, which requires all nations to develop public plans detailing how they would cut carbon emissions through at least 2025. Oddly enough, Trump’s own hand-picked new energy czar, Rep. Kevin Cramer of North Dakota, agrees that his boss can do only so much damage. Cramer, in an interview with me in late May, was notably noncommittal when I asked him if Trump would simply renege on the Paris accord. He noted that Trump has said at a minimum that he’d “renegotiate” it, and he made the point that this is how Trump has approached past business negotiations, starting from an extreme position.

“I think you might see him pivot away” from his hard-line stance on scrapping the agreement altogether, Cramer told POLITICO.

Even Trump himself appears to be conceding some ground on the pact, saying at a minimum he will “rein it in as much as possible.” It all feels rather made-up-as-he-goes-along: Cramer, known as an energy hawk who wants to cut “punitive” fees on oil—but also wants to see more of a federal role for selling power across state lines—says he had spoken to Trump only twice before the campaign tapped him. One was on a radio talk show in early April, Cramer says, and then again a couple weeks later when Trump came to Washington to deliver a foreign policy speech.

In an era in which denial of global warming is still the official platform of the GOP, and the party’s newly anointed leader has repeatedly called it a “hoax,” the fate of the Paris accord under a potential Republican president may well be crucial to the future of the earth’s climate. Formally speaking, Trump can’t just wave a wand and pull the United States out of the Paris treaty; to leave it officially would require the United States to first wait three years, and then give a one-year notice—effectively putting a withdrawal beyond the next presidential election. Nor could Trump hope to renegotiate the international climate accord, which was reached by more than 170 countries after nearly 25 years’ worth of backroom meetings and formal negotiations. A President Trump would not be able to herd all those diplomats back to the table.

What Trump could do, however, is obstruct compliance at home by holding up key appointments, squeezing key agencies’ budgets or taking other executive actions that would have the cumulative effect of slowing down the international momentum Obama has built on climate. Just as Obama is trying to rush through new rules with executive decisions, a President Trump would have the latitude to reverse course on clean energy. This includes possibly approving construction of the Keystone XL oil pipeline, although the company hoping to build it, TransCanada Corp., has said projects like this are not usually structured for the U.S. government to get “a piece of the profits,” as Trump said he wants.

It’s not remotely likely that Trump could succeed in “eliminating” the Environmental Protection Agency, as he says he will do. But he would have a lot of Republican support for sharply cutting its budget. A much steeper hurdle would be to block it from carrying out the authority that Congress has already given it under the Clean Air Act to regulate pollution—which the EPA now says includes emissions from coal-fired plants. This is the heart of Obama’s Clean Power Plan—the biggest tool the administration has to cut carbon emissions. Under the plan, the Obama administration labeled carbon emissions as a pollutant and then sent through the EPA a rule for states to collectively cut heat-trapping carbon emissions from large coal-fired or natural gas power plants by about a third by 2030. A case testing this authority is now in the courts and if the EPA is defeated, it would have a damaging effect on the commitment the U.S. just made in Paris.

“The real risk is not that Trump would pull out of the treaty—but that he would not take the measures to meet the target that Obama committed us to,” says Alden Meyer, director of strategy and policy for the Union of Concerned Scientists. “There is no fear that he could derail Paris. This is unstoppable. … It’s a question of pace and whether we do it fast enough to head off the worst impacts of climate change.”

Thus, in the end, Trump could indeed delay the U.S. commitment by taking actions on the domestic side that would make it harder to rein in our carbon emissions, including expanding oil drilling. This is especially true if the court were to rule against the EPA and the U.S. under his leadership loosened restrictions it’s just set on coal plants.

Such a reversal on climate change has happened before. George W. Bush pulled out of the Kyoto treaty in 2001 shortly after EPA Administrator Christine Todd Whitman pledged to the G8 that the United States was committed to doing its part to meet its aims. That set back climate negotiations for years. But Meyer and others argue that this is a very different era, not least because even developing countries recognize now that it’s in their self-interest to contain climate change lest their economies are harmed by it; U.S. business is on board for the most part in developing green technology; and even climate-change-denying Republicans in Congress are backing renewable energy plans—as they did late last year in extending tax credits for clean energy.

In his North Dakota speech, Trump said he would drop subsidies for clean energy if elected, saying the government “should not pick winners and losers.” But his own party is now backing that approach. “Republicans supported [the subsidy legislation]. Are those same lawmakers going to let him scrap it?” says Meyer.

Jon Pershing is doing whatever he can to ensure that Paris never becomes Kyoto. He has just returned from two days in Bonn, Germany, where he had marathon meetings with officials to develop guidelines to prove countries are making the emissions cuts they have agreed to—including big emitters like China and India. This included determining to what extent American taxpayers will foot the bill to help countries meet these targets.

Pershing, who has had more than 20 years’ worth experience in climate negotiations, insists that the odds are virtually nonexistent that any president—including Trump—could abandon the Paris agreement because he would be going up against a tide of opinion and well-advanced negotiation that includes not just governments but major U.S. companies. Example: Google wants to know where it can source renewable power. Apple is heavily involved after pledging to cut its own carbon emissions—some 38.4 million metric tons worth last year from its global operations. They are among 81 companies that have signed a White House pledge to cut their emissions and use more clean energy. The commitments are not just about addressing global warming. They are responding to consumer demand, drops in solar and other green technologies, concerns over resource sustainability—and wanting to be on the front edge of where the global economy is moving.

“These are major American players. Will this stop given a different administration?” says Pershing. “The world is headed to low-carbon future. How would our guys compete?”

Obama administration officials are also quick to point out that China is now surging ahead in the renewable energy market—and its businesses are reaping the benefits. Global clean energy investment hit a record $329 billion last year and China represented a third of this, according to Bloomberg New Energy Finance.

Much of this growth has been on the back of direct support by the Chinese government—at the same time that it is shutting down coal plants. These subsidies were a key part of the accord, along with cutting carbon emissions. Obama joined 19 other countries in promising to double spending on clean energy in the next five years and, in Japan last week, he and other G7 leaders followed this with a commitment to end most fossil fuel subsidies by 2025.

What Paris represents “is the future of energy,” says Dan Utech, the president’s deputy assistant for energy and climate change. He noted recent sharp drops in solar and wind power prices, representing 67 percent of all new power capacity in the U.S. the past year. “Economically, trillions in new innovations will be made in the decades ahead.” Americans, he says, “clearly” care about being in a position to compete effectively, to become leaders in what is ‘an inevitable transformation.’”

This week, Obama will host Indian Prime Minister Narendra Modi, whom the president credits for helping to seal the Paris agreement. The U.S. government, in return, is helping India–the world’s third biggest carbon emitter—to meet a target to expand its solar capacity by five times in the next six years. Alden Meyer, who worked alongside Pershing in Bonn, says this also represents a big opportunity for American business. India’s energy minister told him the price of LED light bulbs there has dropped from $5 to $1—in just 18 months. “So India is planning to replace all the light bulbs on its streets,” he says. “Who’s going to supply them?”

If Trump is elected, could he succeed in increasing fossil fuel production to the point where the United States would fail to meet the targets to which it agreed in Paris—cutting U.S. emissions by 26 to 28 percent from 2005 levels by 2020? Yes, to a degree. Electricity production counts for the biggest share of U.S. greenhouse gas emissions and 67 percent of that comes from coal, natural gas and petroleum—which is why Obama made the sector a priority. But stiffer government regulations are only part of the reason why companies like Peabody Energy, the nation’s largest coal mining business, have filed for bankruptcy. Market dynamics—and consumer choices—are also at play—and they are much harder for presidents to roll back. Coal has been losing out to natural gas, which produces fewer emissions and is cheaper and more abundant.

“It’s not policy—ultimately it’s about markets,” says Ethan Zindler, an analyst with Bloomberg New Energy Finance. He argues that the United States will achieve the target even without Obama’s Clean Power Plan because gas is cheap and is expected to stay that way, because renewables have gotten much cheaper—and will continue to drop in price—and the renewable energy tax credits that Congress just passed are now on the books for the next five years.

“The contradictory part of Trump’s energy speech was the idea of expanding drilling but also helping coal. Gas is eating coal’s lunch. If you pledge to make gas bigger, you will hurt coal even more.” Zindler ultimately sees the Clean Power Plan as a backstop for an unlikely scenario: that gas prices suddenly rise and coal becomes more competitive again. “If that happens, and we start emitting more CO2, then we would need [the plan] to achieve the Paris goals. But this is not what we think will happen.” So U.S. carbon emissions, he and other analysts say, will continue to drop. It’s just a question of how fast and how aggressively the next president moves to influence that trajectory. Zindler also says that Obama’s earlier regulations, such as one that set a tougher standard for mercury, have already hit the coal industry to a degree that any future regulations can’t unwind.

As early as this fall, at least 55 countries are expected to ratify or otherwise join the historic Paris agreement. And the administration is working hard to flood hundreds of other environmental rules—many aimed at Paris-targeted carbon emissions—through the regulatory pipeline, from chemicals to phasing out hydrofluorocarbons (HFCs). Pershing told POLITICO the White House expects to see through to fruition an update to the little-known “Montreal Protocol,” which would set tougher limits on these pollutants. The Department of Energy is also planning to finalize more than a dozen energy efficiency rules on buildings and appliances this year. Businesses are rushing to conform.

Ultimately, it is the courts, not Trump, that will likely play the biggest role in determining whether Paris is the fait accompli that Pershing makes it out to be. Obama’s Clean Power Plan has been hit with lawsuits from 29 states and coal companies that challenged the EPA’s authority, and the Supreme Court issued a stay in February, temporarily blocking the administration from implementing the rule. Industry groups argued the EPA didn’t give enough consideration to the costs they would bear if the Clean Air Act is enforced. Supporters say the court has already ruled in favor of the EPA’s ability to regulate greenhouse gases as “air pollutants” under the act, in the 2007 case Massachusetts v. EPA.

The United States Court of Appeals for the District of Columbia Circuit will hear arguments in September in the case. Eighteen states and six cities opposed the stay, citing climate change, and many of those—like California—are expected to take their own steps to cut emissions, regardless of who next takes office. Before the stay, 20 states were discussing using carbon trading to meet the EPA guidelines. “California will not slow down our drive for clean air, renewable energy, and the good jobs that come from investing in green technologies,” Air Resources Board Chair Mary D. Nichols said at the time.

Utech argues that the rules will withstand legal challenges because the mandates fall under the Clean Air Act. “We strongly believe it’s on sound technical footing and we’re looking forward to our day in court,” he said. “We think we’re going to prevail and that it will be implemented.”

Congress itself gave the EPA the power to set standards when it passed the Clean Air Act back in 1970. And here too, if a President Trump wanted to roll things back, it would be an uphill battle in Congress to try to overturn the act itself—which has had durable bipartisan support since it was enacted. True, Senate Republicans are trying to pass measures to hurt the EPA’s ability to set and enforce pollution standards. With Trump’s support, they could hamstring its budget and slow walk appointments. But the agency would still have to carry out regulations under existing laws.

The White House—aware that it has only six months left— is once again trying to get new regulations through quickly, ahead of a 60-day period that would allow opponents in Congress to use the Congressional Review Act to overturn them. Obama’s next big move will be to set higher gas mileage requirements for semi-trucks and large pickup trucks and vans, a goal it put off after doubling fuel economy standards for cars during his first term. Observers say it could be in for tough industry negotiations. The administration will also be pushing by September to get American airlines to agree to a “net zero” carbon emissions standard through a global program. These are areas where a President Trump could try to roll back much of what Obama is doing. The hurdle is that once these regulations become law, undoing them requires an extensive rule-making process—or a vote in Congress to eliminate the original power it gave an agency to set standards.

Much more controversial is a limit it set this month on methane emissions from new oil and gas operations. Emitted from power plants, automobile tailpipes and factories, it accounts for nearly 11 percent of U.S. greenhouse gas emissions. The EPA will also be collecting more data from oil and gas producers, with an eye on tougher standards.

It also plans to define by the end of the year “how a federal coal program might be run differently,” Utech said. It has already set a pause button on new coal leases and is creating a federal database to track carbon emitted from extraction on federal land.

Trump seized on these moves in his North Dakota speech, calling the Obama climate rules “death by a 1,000 cuts over regulations.”

“I’m going to free up the coal,” he said, aiming his remarks at Hillary Clinton, who said early on in the campaign that the industry was as good as buried. She has now walked back those comments and has toured West Virginia towns where coal plants have closed.

At a minimum, Trump would have to get a win in the courts against the administration’s Clean Power Plan to dismantle the coal plant regulations. And to eliminate funds for clean energy, as he professes to want, would require a reversal from Congress. In line with the Paris agreement, it just passed five years’ worth of incentives for solar with key votes from Republicans like Iowa Sen. Chuck Grassley, whose state has big wind power potential. Overturning them would require votes from Democrats. “It’s not going to happen,” Utech says.

After being criticized by environmentalists for not doing enough on climate in his first term, Utech stresses that it’s an issue Obama sees as a top priority for defining his time in office. And he has public opinion firmly behind him, with 64 percent of U.S. adults telling Gallup in March they are worried a "great deal" or "fair amount" about global warming.

“We’re going to continue to make progress on this issue. That’s what the American people expect,” says Utech. “Coming out of Paris, it’s also what the rest of the world expects.”

Whether Trump ultimately conforms to those expectations—or continues to resist them—remains to be seen. But if he succeeds Obama, he’ll have a lot of work to do to dismantle the edifice that Pershing, Utech and others are building.