By By Matthew Daly The Associated Press WASHINGTON (AP) - 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.