President Trump's White House victory significantly dimmed the outlook for U.S. EPA's Clean Power Plan. Trump will try to unravel the rule along with other environmental regulations that he deems burdensome.

He has directed EPA to review or rescind the rule, which will take time and face lawsuits from environmental groups. The Trump administration also could try to rewrite a finding that CO2 is a dangerous air pollutant. That would face substantial legal hurdles.

Implementation of the Clean Power Plan has been on hold since the Supreme Court in February 2016 froze the rule until legal battles were resolved. More than half of states and numerous industry groups are challenging the regulation. Dozens of lawyers faced off in the U.S. Court of Appeals for the District of Columbia Circuit in oral arguments in September 2016. If the court issues a decision, parties on the losing side may appeal to the Supreme Court. The court in late April agreed to put the case on hold for 60 days, until the end of June – partially granting a Trump administration request to freeze proceedings indefinitely. Now the judges are considering arguments from both sides on whether to put a long-term hold on the case or simply close it.

The Clean Power Plan case has seen several plot twists. The D.C. Circuit in May 2016 decided to bypass review by a panel of three judges and hear the case en banc -- with the full court. In February 2016, the Supreme Court blocked EPA from implementing the rule after the D.C. Circuit had declined to issue a stay. For many, that signaled doom. But then Justice Antonin Scalia died, leaving an opening on the bench. Scalia had cast the pivotal vote by which the Supreme Court decided 5-4 to halt the Clean Power Plan, giving critics reason to believe justices would torpedo the rule along those same lines.