Health and environmental activists sued the government, arguing that the new regulations inadequately address the threat of the climate crisis. The American Lung Association and the American Public Health Association first filed the suit. Then dozens of other groups signed on and more than 170 amicus briefs were filed in the case revolving around the Trump administration's move to scrap the Clean Power Plan, as Courthouse News reported.

The new Trump rule, touted as the Affordable Clean Energy rule, "will result in some fossil fuel plants running more often and delaying their retirement, which would mean increased emissions of dangerous pollution as compared to the Clean Power Plan," according to the American Lung Association, as Courthouse News reported.

In arguments held virtually that went all day, the panel of judges — two Obama appointees and one Trump appointee — fired questions at the lawyers on a range of topics from U.S. Environmental Protection Agency (EPA) jurisdiction to how coal turns into electricity, as Bloomberg Law reported.

The plaintiffs contend that the administration's Affordable Clean Energy rule will not only allow power plants to make no effort to reduce carbon emissions, but will also allow them to increase other toxic pollutants emitted into the atmosphere. That consequence betrays the EPA's mandate and legal obligations, they argue, as The New York Times reported.

New York Deputy Solicitor General Steven C. Wu said the Affordable Clean Energy plan is unjustified and inadequate to make any significant impact in reducing greenhouse gas emissions.

The case may have far-reaching implications as the Trump administration is arguing that the EPA has an extremely limited amount of authority in the Clean Air Act. That limited scope, the administration argues, means the federal government has neither the authority to set national limits on greenhouse gas emissions, nor the jurisdiction to mandate that states move away from coal power, according to The New York Times.

The plaintiffs in the case argued that the Trump administration's rollbacks were irresponsible.

"It's like choosing a squirt gun to put out a five alarm fire. EPA provides no reasoned explanation of how such a paltry remedy is appropriate given a record showing such an urgent problem," said Sean Donahue, a lawyer representing the plaintiffs, in his argument for the health and environmental petitioners, as Courthouse News reported.

If the Trump administration is successful in the case, it will limit the scope that any future administration has to curtail the emissions from power plants, which are the nation's second largest source of greenhouse gases after transportation. If the administration loses the case, it's expected to appeal to the Supreme Court, making the potential appointment of Amy Coney Barrett high-stakes for environmental policy, according to The New York Times.

"The Trump administration has really taken a go-for-broke approach," said Joseph Goffman, executive director of Harvard University Law School's Environmental & Energy Law Program and a former EPA official under Obama, to The New York Times. He added that if the Trump administration wins, "Then they've really advanced a broader project that the Trump administration has been pursuing to not only repeal individual rules, but to narrow the foundation of the federal government in doing any kind of regulation."