One of the major campaign promises Donald Trump made while running for president was that he would revitalize the moribund coal industry in America. He repeatedly told audiences of miners in prominent coal-producing states that they were going to "start to work again" and that "the coal industry is going to make a very big comeback."

He also touted the potential of a technology, "clean coal," that would ostensibly take existing coal and process it into a cleaner burning form of energy.

While he offered few details, he promised it would be the catalyst the mining industry needed to rebuild from the climate regulations that President Barack Obama imposed.

Now that he's been elected, it's becoming clearer that Trump's detail-light promise to restart Appalachia's faded coal industry was just that: a promise with few details.

The coal industry has collapsed for a number of reasons, chiefly that it's been replaced by cheaper and cleaner sources of power — in particular, natural gas. American domestic use has fallen drastically, with coal now generating less than one-third of U.S. power.

Exports have also dropped off, with the chief importers, China and India, relying mostly on their own stocks. Dozens of mining companies have gone bankrupt, and those that remain are using new technology that reduces their need for workers.

Trump's "clean coal" could — were it real — bring these jobs back.

But clean coal is a largely theoretical technology that likely can't be reproduced on a major scale.

But whether it exists or not, a President Trump will have the ability to push coal if he wants, as Senate Majority Leader Mitch McConnell noted at a conference in Louisville, Kentucky:

“I certainly would like to see the war on coal come to an end. As I’ve said repeatedly over the last few years, the war on coal was not a result of anything Congress passed, there was no new legislation. This was all executive orders or regulations that the president was involved in, unilaterally, on his own.

So we are going to be presenting to the new president a variety of options that could end this assault. Whether that immediately brings business back is hard to tell because this is a private sector activity.

As McConnel noted at the end there: Even if Trump ends the "war on coal," that doesn't mean more jobs.

McConnell displays the same lack of understanding as to why coal has fallen out of favor and, naturally, blames Obama for it. But at least he understands the the U.S. government has little ability to "revive" the coal industry, "immediately" or in the long term, for that matter. Coal has to keep compete on the market, where alternatives like wind and solar are increasingly. Coal's future, then, has already been decided.

It's not just the most powerful man in the Senate who thinks Trump's coal promises are empty. The interim president of the Kentucky Coal Association, Nick Carter, was quoted in the Lexington Herald-Leader expressing the same thoughts. "I would not expect to see a lot of growth because of the Trump presidency," he said. If there is any growth in Eastern Kentucky, it will be because of an improved economy for coal.”

Given the low cost of natural gas, the high cost of mining, and the push toward renewable energy, an increased demand for coal seems unlikely. And with "clean coal" decades away from becoming a reality for consumers, Trump's vow to bring the coal industry back seems that much more hollow.

By lifting regulations on the industry, however, Trump can do a lot of damage to our climate.