The Trump administration has made clear they intend to rollback significant regulations, particularly with regards to carbon emissions and the Clean Power Plan — and Obama-era policy directed to combat human-caused climate change, and pull out of the trans-national Paris Climate accords. In keeping with prior administrations, Trump’s policy proposals have also included rolling back fuel efficiency standards for commercial and private vehicles, reducing subsidies and potentially research for alternative/green energy.
Scott Pruitt, the former Oklamhoma AG and now nominee to head the EPA, is a known and aggressive opponent of federal environmental regulations and has made a career of suing the EPA to halt or rollback regulations. His strategy at this point appears to be the dismantling and reversal of the significant environmental policy progress in the US over the last 40 years. As much of this policy has developed thru EPA rules, sometimes called “green drift,” (i.e., agencies like the EPA adapting and expanding America’s foundational green laws —  the Clean Air and Clean Water acts, the Endangered Species Act, the National Environmental Policy Act — to address new problems), there is quite a bit that could potentially be done. (A few months ago Vox created a good summary of environmental issues.) In the past rapid change in rules have been limited due to the relatively long public comment periods and contentious lawsuits that create a lot of inertia around these policy provisions; however some of this could in theory be undone more quickly if the procedures around these rules are dismantled as well.
Interestingly, like many issues these days, State law also comes into play with regards to environmental rules. In many ways, California has been a leader in environmental law due to its (1) massive size and economy and (2) consistent legislative drive to set a higher burden of environmental regulation. As the landscape is quite uneven across the country, many large companies and organizations (such as vehicle manufacturers) adapt to the more stringent state standards in order to sell products/services nationally.
Like almost all areas, environmental policy is a hot topic and one in great flux. We will continue to post on relevant issues as situations evolve.