Trump’s speech, given at an oil conference in North Dakota, was heavy on big ideas designed to appeal to the fossil-fuel industries but light on specifics.

He said he would “save the coal industry” while at the same time offering full-throated support for the fracking of natural gas, which is largely responsible for the bankruptcies and job-losses being seen across the US coal industry.

Most of Trump's key themes on energy -- eliminating environmental rules and maximising domestic production --  echo those of previous Republican presidential candidates.