There are a few things I understand are killing coal jobs.
1. Automation. More coal can be mined with fewer people.
2. Flat electricity demand. Any external pressure (competition, efficiency) will reduce jobs.
3. Cost competitive natural gas. It's simple economics. If a MW is cheaper from a gas plant than a coal plant, gas it is. Forty years ago coal plants ran nonstop. Now I see those same plants ramp up and down each day. They run but use less fuel.
4. Carbon emissions. This is the closest Gray has to a valid point. The concern over future carbon restrictions will limit any utility's interest in building a new coal plant. They might have a 30-40 year payback, and future carbon restrictions could hurt their future economical. But that isn't Obama, he's merely a reflection of it. It's the global recognition of climate change. Utility executives and financiers are pragmatic. They see the writing on the wall. Trump can't undo this any more than Obama created it.