The president's chief economic adviser is casting doubt on the future of U.S. coal, saying it "doesn't really make that much sense anymore as a feedstock," directly contradicting President Donald Trump's repeated promises to revive the struggling coal industry.

Briefing reporters Thursday night on Air Force One, Gary Cohn singled out natural gas as "such a cleaner fuel." By exporting more natural gas and investing in wind and solar energy, the U.S. "can be a manufacturing powerhouse and still be environmentally friendly," Cohn said.

Cohn's comments were at odds with his boss, who campaigned as coal's champion and decried what he and other Republicans called a "war on coal" by former President Barack Obama.

As president, Trump has unraveled a number of Obama-era energy restrictions, including a landmark plan to restrict climate-changing emissions from coal-fired power plants. Trump also has reversed an Obama plan to prevent coal mining debris from being dumped into nearby streams and lifted a moratorium on coal-mining leases on federal lands.

Sen. Joe Manchin, D-W.Va., a longtime coal advocate, said he was taken aback by Cohn's remarks, which sounded more in line with the Obama administration than Trump.

"I completely disagree with his statement," Manchin said, adding that he plans to meet with Cohn "to explain the role that coal has and will continue to play in making this country great."

Melinda Pierce, legislative director for the Sierra Club, the nation's largest environmental group, said Cohn's comments were accurate.

"Coal is increasingly not competitive as the market, the international community and public opinion reject this dirty fossil fuel that makes our families sick, pollutes our air and water and threatens our climate," Pierce said.

"The Trump administration's policies are completely at odds with these facts and need to catch up to reality instead of putting polluter profits ahead of the health of our communities," she said.

That's unlikely to happen.

Throughout the presidential campaign, Trump railed against the Obama administration policies as he campaigned in economically depressed swaths of states like West Virginia, Pennsylvania and Ohio. Trump won all three states and swept eight of the top nine coal-producing states.

The New York billionaire has frequently celebrated his popularity in coal country.

At a ceremony in March, Trump was flanked on stage by more than a dozen coal miners as he signed an executive order that eliminated a host of Obama-era restrictions on fossil fuels, breaking with leaders across the globe who have embraced cleaner energy sources.

"That is what this is all about: bringing back our jobs, bringing back our dreams and making America wealthy again," Trump said.

The miners "told me about the efforts to shut down their mines, their communities and their very way of life. I made them this promise: We will put our miners back to work," Trump said. "My administration is putting an end to the war on coal."

Trump's promise runs counter to market forces, including U.S. utilities that have converted coal-fired power plants to cheaper, cleaner-burning natural gas. Democrats, environmental groups and scientists said Trump' executive order ignores the realities of climate change.

While Republicans have blamed Obama-era environmental regulations for the loss of coal jobs, federal data shows that U.S. mines have been shedding jobs for decades amid increasing automation and steep competition from natural gas.

Another factor is the plummeting cost of solar panels and wind turbines, which now can produce emissions-free electricity cheaper than burning coal.

According to an Energy Department analysis released in January, coal mining now accounts for fewer than 75,000 U.S. jobs. By contrast, renewable energy -- including wind, solar and biofuels -- accounts for more than 650,000 U.S. jobs.