President Donald Trump’s Environmental Protection Agency issued new regulations this month that will save many coal and natural gas power plants from closure. To prevent them from being unnecessarily decommissioned, the agency used a clever new argument that will help the new standards hold up in federal court.

The Clean Air Act grants the EPA legal authority to issue regulations for any substance it determines can “reasonably be anticipated to endanger public health or welfare.” Since the legislation was enacted, the EPA has used it to regulate universally recognized pollutants such as carbon monoxide, sulfur dioxide, lead, and particulates.