For the past five years, solar and wind energy have exploded in popularity in the  United States. Since the election of Donald Trump, energy analysts have been trying to figure out if that trend will continue.

Some analysts argue that the trend is irreversible. The cost of solar and wind power are falling so fast that they will soon beat fossil fuels on price alone, regardless of what the federal government does. Since 2008, the price per watt of utility-scale solar energy has fallen by 64 percent. Even Walmart puts solar panels on its roofs now.

Others argue that the Obama administration has stoked this sense of technological inevitability—and that if the Trump White House were to heavily subsidize coal or natural gas, or permanently disrupt the EPA’s ability to regulate greenhouse gases, the rise of renewables might falter.

Now the man whose administration shaped that energy policy has weighed in on the debate. In a policy paper published Monday in the major academic journal Science, President Barack Obama argues that—no matter what his successor does—the growth of solar and wind energy is irreversible.

“Putting near-term politics aside, the mounting economic and scientific evidence leave me confident that trends toward a clean-energy economy that have emerged during my presidency will continue,” he writes. “The economic opportunity for our country to harness that trend will only grow.”

Why is the president so sanguine about clean energy? He lays out four reasons.

First, he says that the United States has proven that an advanced economy can grow without greenhouse gas emissions growing too—a phenomenon that in energy jargon is called decoupling.

“CO2 emissions from the energy sector fell by 9.5 percent from 2008 to 2015, while the economy grew by more than 10 percent,” he writes. (This decline has been due in some part to the replacement of coal-generated electricity with natural-gas burning, but more on that in a bit.)

Second, many businesses will continue to make energy-efficiency investments, he says—though he adds that some of these investments were only possible thanks to federal energy-efficiency standards. Third, the power sector is already switching electricity plants from coal to natural gas and is unlikely to migrate back to coal. Finally, the entire world is moving toward clean energy and investing in renewable development, he says. If nothing else, it will tug the United States along with it. (Just last week, China committed to spending at least $360 billion on renewable energy by 2020.)

It’s the third time in a week that Obama has taken to a preeminent journal to defend his legacy. On Thursday, he wrote a commentary for the Harvard Law Review on the chief executive’s role in criminal-justice reform. The next day, he warned in The New England Journal of Medicine against repealing the Affordable Care Act without a replacement.

You could understand this publishing streak as the wonk president taking a final, well-credentialed bow—or as Obama, the great establishmentarian, making one last appeal to the institutions that made him and bolstered his presidency.

To my eye, the most interesting part of the president’s paper is his point about natural gas and power generation. In 2016, natural gas surpassed coal and became the largest generator of electricity in the United States. Obama argues, basically, that the fuels won’t switch back. In this argument he makes two different references to “near-term federal policy.” It seems he is talking about Trump without ever actually saying “Trump”:

Because the cost of new electricity generation using natural gas is projected to remain low relative to coal, it is unlikely that utilities will change course and choose to build coal-fired power plants, which would be more expensive than natural gas plants, regardless of any near-term changes in federal policy. Although methane emissions from natural gas production are a serious concern, firms have an economic incentive over the long term to put in place waste-reducing measures consistent with standards my Administration has put in place, and states will continue making important progress toward addressing this issue, irrespective of near-term federal policy.

The president is making two arguments by allusion here. First, he is warning that even if the Trump administration soon subsidizes coal mining, those subsidies will not last long enough to justify new coal power plants. Second, he is asserting that the EPA’s recent restrictions on natural-gas leaks—a regulation that Republicans in Congress have sworn to repeal— are in the best interest of the entire energy industry.

Natural gas is primarily composed of methane, a greenhouse gas. It can trap more than 25 times as much heat as carbon dioxide, though it only remains in the atmosphere for about a decade on average. (CO2 can hang around in the atmosphere for 10 centuries.) The Obama administration’s methane rule mostly aims to prevent natural gas from escaping into the atmosphere during the fracking process.

Rob Barnett, a senior analyst for energy policy at Bloomberg Intelligence, agreed with most of the president’s trend-spotting.

“Even if Trump’s administration is able to provide regulatory relief to the coal industry, there isn’t likely to be much interest in building new coal-fired power plants in the U.S.,” he told me in an email. Natural gas edges out coal both from a fuel-price and a long-term investment perspective.

But he warned that fossil-fuel emissions haven’t gone down in every sector. Nationally, gasoline demand is slightly up since Obama’s presidency began.

“Even in California, where regulators have thrown the kitchen sink at carbon emissions, gasoline consumption and emissions have risen six percent since 2012,” Barnett said. “Reversing the current trend may require greater regulatory focus.”

It makes sense that Obama would now argue for his legacy’s irreversibility—arguing from inevitability has always been a great aspect of his politics, in energy and otherwise.

Obama’s energy policy has been in great part about pushing private investment into the renewable-energy industry. Domestically, he has tried to communicate, using every available lever of the federal government, that a clean-energy transition was coming. Globally, his administration has seen climate treaties as one more crucial investment signal. Even as he was negotiating the Paris Agreement, Secretary of State John Kerry described it as principally a sign to the world’s companies that renewable energy (and climate mitigation generally) was a growth market.

“We are sending literally a critical message to the global marketplace,” Kerry said on December 12, 2015, from the Paris talks. “One-hundred-eighty-six nations [are] saying to global business in one loud voice: We need to move in this direction. And that will move investment.”

As Obama leaves office, he is communicating his message about the inevitability of clean energy again. Millions of Americans—including the more than 700,000 employed in the renewable-energy industry—are hoping he is right.