Austin, Tex. — Donald J. Trump made many important campaign promises on his way to victory. But saving coal is one promise he won’t be able to keep.

Many in Appalachia and other coal-mining regions believe that President Obama’s supposed war on coal caused a steep decline in the industry’s fortunes. But coal’s struggles to compete are caused by cheap natural gas, cheap renewables, air-quality regulations that got their start in the George W. Bush administration and weaker-than-expected demand for coal in Asia.

Nationwide, coal employment peaked in the 1920s. The more recent decline in Appalachian coal employment started in the 1980s during the administration of Ronald Reagan because of the role that automation and mechanization played in replacing miners with machines, especially in mountaintop removal mining. Job losses in Appalachia were compounded by deregulation of the railroads. Freight prices for trains dropped as a result, which meant that Western coal — which is much cleaner and cheaper than Eastern coal — could be sold to markets far away, cutting into the market share of Appalachian mines. These market forces recently drove six publicly traded coal producers into bankruptcy in the span of a year.

Mr. Trump cannot reverse these trends.

For Mr. Trump to improve coal’s fate would require enormous market intervention like direct mandates to consume coal or significant tax breaks to coal’s benefit. These are the exact types of interventions that conflict with decades of Republican orthodoxy supporting competitive markets. Another approach, which appears to be gaining popularity, is to open up more federal lands and waters to oil, gas and coal production.