President Trump in an executive order directed the Department of Defense to buy electricity from coal-fired power plants, reviving a fuel source in sharp decline. Coal’s share of U.S. electricity generation has plummeted from 50% in 2000 to roughly 17% in 2025 as natural gas and renewables gain ground. Coal is relatively inexpensive to produce but is considered the dirtiest fossil fuel, releasing soot air pollution and nearly twice the planet-warming carbon dioxide as natural gas.