On the contrary, I'm intimately familiar with coal, as it is a major Alabama mining industry (think: Drummond). We even drill and produce natural gas from underground coal deposits (check out DOM on the stock market).
Our coal infrastructure is here. We can ramp up production to fantastic levels with no problem.
I know about continuous mining. I don't buy doubling output with "no problem." Further, most of the target power plants are designed to burn gas. Converting them to coal is not quick or easy, however doable it might be. The necessary distribution infrastructure is problematic too. Then there's getting the real estate near a rail line in an urban area for dealing with coal storage and delivery near the transmission grid or else installing the delivery lines. That isn't quick or easy either.
By contrast, nuclear plants are on their way to becoming a local drop-in installation, and far easier to tie into the existing transmission grid. Because they are small, the system is less subject to single-point failures. Their design makes them a very difficult target for terrorists too.