The Supreme Court on Monday has a chance to remind the Environmental Protection Agency that there are limits to its power.

During the Obama administration, the EPA made an amazing discovery: It suddenly found the power to establish Soviet-style central planning of the nation’s electricity sector in a provision of the Clean Air Act that virtually nobody had ever noticed. Now the Supreme Court will finally decide whether that power was real or just a magic trick pulled off by the radical environmentalists. 

In 2015, the EPA published the Clean Power Plan — an ambitious strategy to shut down coal and natural gas and force states to make the transition to renewable sources of electricity. 

The plan was shot through with statutory and constitutional problems, but the EPA was swinging for the fences. 

Obama officials knew that the plan would be lucky to survive court challenges and would be dead as fried chicken if Democrats lost the next election.

They did, and in 2019 President Trump’s EPA repealed the Clean Power Plan and replaced it with a new rule that focused on reducing carbon emissions from coal plants without necessarily shutting them all down and forcing all states to adopt some version of California or New York’s abusively expensive electricity system. 

On the very last day of Mr. Trump’s presidency, however, the powerful D.C. Circuit Court of Appeals vacated the Trump rule. Hesitating to swing for the fences again, the Biden administration almost immediately asked the D.C. Circuit to hold back on reinstating the Obama-era rule, while it tried to figure out its next moves.

One crucial question for Mr. Biden’s climate agenda is whether the EPA really has the power it thought it had discovered in the Clean Power Plan. That question is now before the Supreme Court in the case of W.Va. v. EPA, which is scheduled for oral argument Monday.

At one level, the case deals with an arcane technical question: What is the meaning of “best system of emissions reduction” under Section 111(d) the Clean Air Act? 

For decades environmental lawyers had assumed that like the act’s other, similar-sounding technology standards, BSER was just a reference to some mundane technology that polluting facilities install to clean up their emissions, like a scrubber on a smokestack. 

It also didn’t matter much, because Section 111(d) is unrelated to any major Clean Air Act program and has been used mostly for solid-waste incinerators, which is why almost nobody had ever noticed it before.

In a fiendishly clever move, however, President Obama’s EPA realized that “best system of emissions reduction” could just mean the entire society, including your decisions about how much electricity to use at what hour of the day in your own house — all as an extension of the EPA’s power to regulate emissions from coal plants. 

If that sounds crazy, the way this case made it to the Supreme Court is even crazier. The case does not involve a challenge to the Clean Power Plan, but rather to Mr. Trump’s repeal of it, which the D.C. Circuit tossed out in a masterpiece of sophistry.

Under Chevron v. NRDC, agencies are supposed to defer to agency interpretations of ambiguous statutory terms, including the Trump repeal’s interpretation of BSER.

Yet in reaffirming that BSER does not extend beyond the polluting facility, Mr. Trump’s EPA pointed out the term had never been considered ambiguous before 2015. That is something the D.C. Circuit could not abide, so it bounced the Trump repeal back to the agency — now, conveniently, in Biden’s hands — to have it admit the term is ambiguous and then tell the world what it means, so that then the court could defer to the agency’s interpretation.

The Supreme Court is unlikely to find all this trickery quite as amusing as radical environmentalists did. The conservative majority has been itching for an opportunity to reimpose some of the separation of powers that has been eroding for decades as the administrative state absorbs increasingly unlimited and unaccountable power. 

The high court could decide the case purely on the basis of statutory interpretation. It could also yank the administrative state’s chain, and establish that Congress does not hide sweeping delegations of legislative power in vague little provisions of law to lie dormant there for decades, waiting for some nameless, faceless bureaucrat in Washington to decide that the time has come to turn the world upside down.