The Ghost of Antonin Scalia
The legal challenge to the Clean Power Plan essentially contends that the executive branch doesn't have the power to intepret laws passed by Congress in new ways based on new information. It's a sort of specific application of legal originalism that Justice Scalia, may he rest in peace, invoked in joining four other justices in staying the Clean Power Plan last year.
Environmentalists had hoped a swift resolution to Scalia's death would strengthen the Clean Power Plan against a court challenge, but his ghost continues to haunt Obama: yesterday a judge invoked a Scalia precedent that suggests Congress, not regulators, must be the source of decisions with "economy-wide" impacts.