Since assuming office in January, President Donald Trump – with the support of Congress – has stated his intention to roll back “burdensome” U.S. environmental regulations. The White House and Congress aim to reverse several of President Obama’s regulations on air and water pollution, land use, and greenhouse gases emissions. But the new President may face challenges to reversing certain existing U.S. climate, environmental, and energy-related regulations.

Thanks to a law called the Congressional Review Act, the Republican Congress has exercised its authority to roll back several key regulations that were published in the waning days of the Obama Administration, including a law limiting methane emissions for oil and gas activity on public land; one requiring oil, gas and mining companies to disclose their payments to foreign governments; and another protecting waterways from coal mining operations. But Congress’s authority extends only to regulations that were promulgated within the past few months. For those regulations that were promulgated longer ago, including the Clean Power Plan regulating greenhouse gas emissions from power plants, the Administration’s options are more limited. President Trump cannot by executive order abolish environmental statutes delegating broad powers to the U.S. Environmental Protection Agency. The President can order any agency to reconsider a rule, but agencies may alter their rules only if they justify departure from the record supporting their original rule. Further, any efforts to change laws protecting the environment generate strong backlash—and lawsuits—from interest groups. And while Congress could enact legislation to remove the underlying statutory authority for certain regulations, there is likely to be strong opposition from certain members of Congress to any such effort.

The new Administration may also encounter opposition from segments of industry if it seeks to rescind environmental rules that are already final and partially implemented, especially where the relevant industry already has invested sunk costs in compliance efforts, or where some companies obtain a competitive benefit from the rule. President Trump has articulated an “industry-friendly” administrative approach, and can be expected to respond accordingly where business interests resist changes that could lead to additional expense or market uncertainty.

Ultimately, a determined and united effort by President Trump and Congress can mitigate, but not eliminate, complex regulatory initiatives of the last eight years. The President’s efforts to do so will be complicated and time-consuming, with battles waged in the media, the White House, Congress, the agencies, and the courts – potentially creating significant uncertainty for industry in the interim. Environmental regulations will face rollbacks, but the Administration’s efforts will be tempered by legal barriers and opposition from some in industry as well as the environmental and public health community.