The Obama administration interpreted its authority under the act ambitiously. Its Clean Power Plan set state-by-state emissions limits and authorized states and utilities to engage in a range of strategies to meet those targets — capturing carbon emissions and storing them underground, emissions trading, fuel switching (replacing coal with cleaner natural gas and with renewables like wind and solar) — anything to wean their economies off coal and diversify the energy supply. The Trump plan jettisons the state limits and asks only for modest retrofits at individual plants.

To put it simply: The Obama plan would have encouraged imaginative thinking and new approaches. The Trump plan plugs leaks. (Perversely, it could also in some cases increase emissions by making power plants more efficient and therefore able to run longer.)

Mr. Wheeler says that Mr. Obama engaged in statutory overreach and that Mr. Wheeler’s narrow reading of his authority under the Clean Air Act is the only legally defensible one. The act, he says, gives the E.P.A. power to fix individual plants, not upgrade the grid as a whole. Many others beg to differ, and attorneys general in New York, California and other states, plus a host of environmental groups, plan to sue on the grounds that the Trump rule artificially narrows what they believe is the agency’s authority to adopt a systemwide approach to emissions control.

It is entirely possible, indeed likely, that the question of what the E.P.A. can and cannot do will eventually come before the Supreme Court in what Jody Freeman, a professor and environmental expert at Harvard University, has predicted will be “a blockbuster” case. Brett Kavanaugh, whose appointment has strengthened the court’s conservative wing, once described the Clean Air Act as a “thin statute,” not designed with greenhouse gases and climate change in mind. The great fear among climate activists is that by upholding Mr. Wheeler’s cramped view of the agency’s authority, the court could effectively foreclose more aggressive action by the E.P.A. in the future.

The demolition job on the Obama climate legacy continues: the rules limiting methane emissions from oil and gas wells, the climate agreement in Paris, now the clean energy plan. Next on the hit list? Probably Mr. Obama’s fuel economy standards. A rule now in the making would essentially freeze those standards at about 37 miles per gallon, well short of the 54.5 miles per gallon Mr. Obama ordained near the end of his administration.