(I can't speak to the mechanics of coal extraction, so I'll skip that topic entirely. I probably should know more, given that my grandfather was a coal miner...)

The boom in combined cycle generation (which uses only NG) is the main reason, IMO. A few data points to illustrate this:

Fuel type Fuel efficiency
Coal 32-42%
Nuke 38%
Simple NG turbine 32-38%
Combined cycle NG 60%

A CC gas plant is nearly TWICE as efficient as coal. That is big bucks. When the NG prices dropped, it became a simple economic choice. Coal was no longer as attractive an option for generating power. Even nukes are having trouble staying competitive. (The other take home message here is... holy crap we waste as much as 2/3 of the energy in this process?!?)

Coal has other disadvantages, too. In order to respond to a "call" for power (which can provide as little as 15 minutes notice), the boilers need to stay hot. That means they burn coal for the hell of it--and let 100% of the energy go (ie, no power is generated). NG is a flip of the switch to start generating. Coal plants are also among the oldest units in the fleet. When they were front line baseload plants, they could afford certain inefficiencies. But as they age and start to fall into intermediate/peaking plant status, coal really starts to take it on the chin. They take more staff to operate and maintain, require more space, and other downsides.

All that said, I won't disagree that coal has a target on its back. It is getting hit from multiple sides (air emissions, coal pile runoff, ash storage, greenhouse gas, mercury, etc.) But I'd say that it's more a matter of the final nail in the coffin instead of the killing blow. In the end, it's economics that is driving this. And that's also reflected in what type of facility that utilities are building. Take a look at [http://www.eia.gov/todayinenergy/detail.cfm?id=15751]. I'm sure there's a more comprehensive data set, but that was one of the first links I found. In short, no one is building any new coal plants. It is ALL combined cycle gas right now. Honestly, it flies in the face of the utilities' typical approach of having a diverse fleet of generation types, but they must know something.

IMO, Trump is being disingenuous with his claim that he'd reopen the mines. There's simply no one to sell the coal to.