Donald Trump has been a major supporter of the coal industry since he entered American politics and donned a hard hat at his “Trump Digs Coal” rally in 2016. It’s been part of his attempt to build an image as a populist, and he’s repeatedly said he’s going to revive the industry and bring back coal jobs. It was apparently with this goal in mind that the president last week ordered the Pentagon to purchase coal energy.

“I will sign an executive order that directs the Department of War to work directly with coal plants on the new power purchasing agreements, ensuring that we have more reliable power and stronger and more resilient grid power and we’re going to be buying a lot of coal through the military now,” Trump said at a signing ceremony last Wednesday.

The coal industry has been in decline for well over a decade, partially because natural gas started out-competing coal after the fracking boom. At the same time, the cost of renewable energy has plummeted over the past 15 years, making it cheaper than coal energy. In short, coal has become one of the most expensive forms of energy in the U.S.