One by one, the artifacts of President Barack Obama’s rule by administrative fiat are tumbling.

The latest is his signature Clean Power Plan that EPA Administrator Scott Pruitt says he’ll begin the arduous process of unwinding.

The first year of Donald Trump’s presidency has been characterized — despite his bumptiousness — not by executive overreach, but executive retrenchment. The populist Trump has operated within constitutional lines better than his technocratic predecessor, who used tendentious readings of the law and sweeping bureaucratic actions to impose his policies on immigration, health care, college campuses and the environment.

The Clean Power Plan, which sought to reduce US carbon emissions to 32 percent below 2005 levels by 2030, was government by the administrative state on a scale that has never been attempted before. The EPA took a dubious reading of a portion of the Clean Air Act (Section III, which arguably prevented the agency from taking this action rather than empowered it to do so) and used it to mandate that the states adopt far-reaching plans to reduce carbon emissions, under threat of the loss of federal highway funds.

The legal foundation of the Clean Power Plan was so rickety that the Supreme Court took the extraordinary step of blocking its implementation pending all the lawsuits against it.

The presumption of the plan was jaw dropping. The EPA usually targets pollutants; carbon dioxide isn’t one (though the Supreme Court erroneously said it meets the definition in the case of Massachusetts vs. EPA).

The EPA has always regulated specific power plants; in this scheme, it went “outside the fence” to mandate broader actions by the states, e.g., the adoption of quotas for renewable energy. The EPA once considered its mandate to be protecting clean air and water for Americans; with the Clean Power Plan, it sought to adjust the global thermostat for the good of all of humanity.

The last gets to the absurdity of the plan on its own terms — it did virtually nothing to affect global warming. As Benjamin Zycher of the American Enterprise Institute points out, the Obama administration’s Climate Action Plan (which includes the Clean Power Plan) would reduce the global temperature by 15 one-thousands of a degree by 2100.

The point wasn’t to fight climate change per se, but to signal our climate virtue in the hopes of catalyzing action by other nations and, not incidentally, to hobble the US coal industry in favor of more politically palatable sources of energy, namely wind and solar.

Whatever the merits of this agenda, as a first-order matter, it must be enacted lawfully and not instituted by strained legal interpretations alone. In congressional testimony arguing the Clean Power Plan is unconstitutional, liberal law professor Laurence Tribe noted that the Supreme Court has said Congress doesn’t “hide elephants in mouseholes.”

If Congress had authorized the EPA to remake the nation’s energy economy we’d presumably be aware of it and recall an impassioned congressional debate over this radical and costly change. Here, the opposite is true. Congress has declined to enact laws limiting carbon emissions, including when Democrats held both houses of Congress under Obama.

If the future of the planet is at stake and it requires a generational effort to save it, surely it’s not too much to ask that a statute or two be enacted by Congress explicitly committing the country to the task. Yes, this requires wining elections and gaining democratic assent, but such are the challenges of living in a republic and a nation of laws.

In his impatience with Congress and his administrative imperiousness, Obama dispensed with all that. What he imposed unilaterally is subject to unilateral reversal.

The rollback will encounter its own regulatory and legal obstacles but can be achieved more readily than if Obama had been able to (or bothered to) write a swath of his legacy into law.

Twitter: @RichLowry