President Trump has promised to revive coal's flagging fortunes. Is it possible? Here's everything you need to know:

How big is the coal industry?

Coal represents just a sliver of the American economy. At its peak, in 1923, coal employed 883,000 workers. Today, about 53,000 people work in coal mining — less than the number of people who work at nail salons, bowling alleys, or Arby's. The decline of coal has been precipitous: In 2010, the U.S. had 580 coal-fired power plants providing 45 percent of the nation's electricity generation. Today, there are fewer than 350 coal plants responsible for about 30 percent of the country's electricity. Nevertheless, coal continues to have an outsize environmental and political impact. Coal is the country's leading source of carbon emissions that contribute to climate change. The American Lung Association believes that the effects of coal pollution kill about 7,500 Americans every year. Burning coal releases fine particulates into the air — tiny particles and liquid droplets of toxic substances such as sulfur dioxide, nitrogen oxide, mercury, lead, and other heavy metals. Inhaled, they contribute to respiratory conditions like asthma, heart problems, and cancer. These same airborne pollutants also settle in the oceans, which is why coal is a leading contributor of toxic mercury in seafood. "There's no reason to think the fortunes of the coal industry are going to change anytime in the future," said Noah Kaufman of Columbia University. "Coal is an industry in decline."

Is that solely because of environmental reasons?

There are economic reasons, too. Demand for coal has plummeted over the past decade amid a flood of cheap natural gas from the U.S. fracking boom and advances in wind and solar energy. American coal production dropped 27 percent between 2011 and 2016, with the combined value of the country's four biggest coal companies falling from $33 billion to $150 million. Nonetheless, the promise of coal jobs remains potent in states like West Virginia, which has been devastated by the coal bust. President Trump made revitalizing the industry a centerpiece of his 2016 campaign, blaming Obama administration environmental regulations for killing coal jobs.

What has Trump done?

True to his word, President Trump has tried to use federal power to revive the coal industry. Many of the White House's actions closely mirror a policy wish list submitted early in the administration by coal tycoon Robert Murray, who contributed $300,000 to Trump's inauguration. That includes withdrawing from the Paris climate change agreement and scrapping Obama's Clean Power Plan, which aimed to cut carbon emissions from power plants by 30 percent by 2030. The White House has also eased restrictions on the dumping of toxic coal ash in streams and waterways, lifted a moratorium on new coal leases on federal land, and killed a federal study on the health impacts of mountaintop-removal coal mining. It has reportedly proposed lifting a requirement that coal plants install equipment reducing toxic mercury emissions. "We have ended the war on beautiful, clean coal," Trump declared during his first State of the Union Address, in 2018.

Are coal jobs coming back now?

Not really. Only about 1,300 new coal jobs have been created during Trump's presidency so far, and Trump's efforts haven't reversed the long-term problems facing the industry. Even after the rollback of the Clean Power Plan, the White House expects the percentage of energy generated by coal to decline by 20 percent between now and 2030. Thirty-six coal-fired plants have been retired since Trump was elected, and 30 more have announced they will close.

Why the obsession with coal?

The electoral map. For most of the 20th century, the Democrats' alignment with labor unions such as the United Mine Workers helped them reliably win in the coal country of Appalachia. But the party's embrace of environmentalism — as well as its deepening culture divide with white, rural Americans — has put coal states such as West Virginia and Pennsylvania in play. Coal also remains a powerful cultural totem: The image of the hardworking coal miner ranks with the cowboy as an icon of American masculinity. Marybeth Beller, a political science professor with West Virginia's Marshall University, says past elections show that many voters "support candidates who demonstrate support for the coal industry, whether or not that support actually increases jobs."

Can coal jobs be replaced?

There are efforts underway to retrain coal workers for jobs in renewable energy or other industries. More than 260,000 Americans already work in the solar power industry, which has nearly tripled in size since 2010. The plains of Wyoming, the nation's largest coal producer, are seen as a natural fit for the burgeoning wind power industry. Many renewable-energy companies even pay for retraining. But miners have largely rejected the idea, betting that coal will be revived. "I think there's a coal comeback," said 33-year-old Mike Sylvester, son of a coal miner in western Pennsylvania. "I have a lot of faith in President Trump."