After few mentions of energy and environmental policy during the first debate, it’s likely the Republican presidential candidates will face questions about the Clean Power Plan during the second presidential primary debate Wednesday night.

Introduced just days before the first Republican presidential primary debate, the Clean Power Plan is an expansive plan that sets carbon emissions limits on power plants. It forces the states to submit plans to the Environmental Protection Agency to cut their greenhouse gas emissions, which most climate scientists blame for driving manmade climate change, by one-third by 2030.