…in defiance of existing law (to say nothing of common sense), the government could run its vehicles on fuels such as liquid coal, even though they’re dirtier than conventional fuels.

Some more detail on that:

Coal-to-liquid technology liquefies coal into conventional fuel for diesel, jet, or car engines. The process itself is expensive, and it also requires large energy inputs that are often derived from fossil fuels that release C02, along with large water inputs. This costly process produces gasoline that releases C02 when it is burned.

From production to combustion, CTL fuel could release as much as 2.5 times as much greenhouse gas into the atmosphere as conventional diesel fuel, according to an analysis by the Argonne National Laboratory cited by David Hawkins of the National Resources Defense Council.
americanprogress.org