Trump at an event in West Virginia in 2016. (Animation from CNN video)

President Trump doesn’t have a great track record of explaining complicated issues correctly. For example, he’s repeatedly claimed that Hillary Clinton “bleached” or “acid-washed” her email server, apparently thinking that her staffers’ use of the free software BleachBit somehow involved actual bleach.

So it’s understandable that the explanation of “clean coal” he offered during his Phoenix speech on Tuesday would similarly miss the mark.

“We’ve ended the war on beautiful, clean coal,” Trump said of his first seven months in office, “and it’s just been announced that a second, brand-new coal mine, where they’re going to take out clean coal — meaning, they’re taking out coal. They’re going to clean it — is opening in the state of Pennsylvania, the second one.”

That’s not correct. But it’s not as wrong as it sounds.

It’s useful to rewind a bit.

It didn’t take long for Trump to realize that coal miners would play a useful role in his campaign rhetoric. He centered his arguments against the D.C. establishment on the idea that workers — especially white working-class workers — had suffered at the hands of the elite decision-makers. Coal miners and manufacturing employees were the most tangible way of making that case. Factory workers had suffered at the hands of bad trade deals, Trump offered, and coal miners thanks to anti-coal environmental regulations.

Trump’s position on the environment, like much of his politics, harks back to the 1970s and 1980s. We need clean air and water, he likes to say, but he rejects the idea that the environment is at risk from climate change that’s been exacerbated by human activity. There are two ways in which coal isn’t “clean.” The first is that burning it releases gases and particulate matter that’s harmful to human health. The second is that burning it releases greenhouse gases like carbon dioxide that enter the atmosphere and help prevent heat from escaping into space, slowly warming the planet.

Trump doesn’t generally distinguish between those two things. He simply uses the term “clean coal” as though to suggest that we’re going to start mining some new form of the mineral that avoids one or both of the problems identified above.

“You see what’s happening with coal,” he said in June. “Coal is coming — clean coal. We love clean coal. And it’s coming back.”

He uses “clean” here the way he uses “beautiful” in other contexts: as a modifier to vaguely strengthen his point.

In Phoenix, though, he actually explained what he meant: “They’re taking out coal. They’re going to clean it.” And that is actually what the term is meant to mean.

“Clean coal” isn’t “coming back” because “clean coal” never existed. It’s a marketing term, introduced about a decade ago as concern about global warming began to mount. At the time, advocates of the use of coal for power generation began using the term to refer to a process, not a product, that would result in fewer harmful emissions. Generally, references to “clean coal” are references to what are called “carbon capture and storage” processes, or CCS. CCS does what it says on the label: Captures the carbon dioxide emitted from burning fuel and stores it somewhere, as you might store the byproducts of other forms of energy.

This technology is still new and hasn’t been broadly implemented. In April, the Department of Energy announced that a CCS plant in Decatur, Ill., had begun capturing carbon dioxide from burning coal and injecting it into a saline reservoir. There’s enough space in the reservoir for 50 years of carbon dioxide storage.

That’s certainly better for the planet than releasing the carbon dioxide into the atmosphere. But it’s also necessarily more expensive than burning coal without capturing the emissions, at a time when prices for other methods of generating energy — burning natural gas, using wind turbines and solar — have been steadily dropping.

It’s important to note that one of the primary recent challenges to the coal industry has been the growth of the natural gas industry. Innovations in hydraulic fracturing — fracking — led to a boom in natural gas production, dropping prices. Energy producers switched over to natural gas since it was competitive in price with coal but didn’t have the same emissions. Trump has also championed the fracking industry without recognizing this conflict.

Trump at least acknowledges that the coal that’s being mined isn’t just suddenly somehow emerging as some clean, environmentally friendly product. He’s not the first to do so; both Presidents George W. Bush and Barack Obama hailed clean coal as a way of splitting the difference between appealing to workers in coal country and recognizing the problematic emissions that result from burning coal. Using the term “clean coal,” though, highlights the economic challenge of continuing to rely on coal for energy production, if you also want to address the problem of global warming — a challenge that’s much more significant for Trump, in this era of cheaper alternate energy sources, than it was for his predecessors.

His championing of new coal mines also deserves a little more context. He celebrated a new mine that opened in June in Pennsylvania. But, as NPR explained, that mine produces a type of coal used for steel manufacturing, not for energy production, and was made feasible in part thanks to a disruption in supplies from Australia. The same company is planning to reopen a mine that had been closed five years ago. The reopening process also began in October — when Obama was president.

But at least Trump acknowledged that coal isn’t inherently clean! That is a small step toward accuracy on the subject that, so far, has mostly been lacking.