I thought the main reason diesel cars are rare in the US is because of our stricter smog standards?
Regardless, Trump appointed an oil evangelist to head the DOE, and no one knows whether that was out of ignorance or spite. So his goals are set a lot further than a one decade rollback but we'll see how far we can plummet.
Personally, it's fracking and coal mining that I'm more worried about, since it's mostly rural, poor people who get their groundwater shit on by industrial waste and they can't afford the extra treatment costs. If it wasn't for federal regulations, most water systems would just use a cheesecloth.
The one good thing about Trump being elected is that the EPAs biggest priority right now is water quality and I'm betting we'll see something far worse than Flint/Hurricane Katrina happening in conservative states, assuming the EPA brings regulations down to what Trump is hoping for. Which will hopefully make people wake up and realize that the government actually protects you at times.