Barack Obama decided that the 1992 Clean Air Act gave the Environmental Protection Agency the authority to force states to regulate carbon dioxide emissions from power plants.

He also expanded the Clean Water Act with a regulation called "Waters of the United States," which aimed to give the EPA regulatory control over land if sometimes it holds standing water.

The running theme of the Obama EPA was expanding the agency's reach and multiplying its responsibilities. This campaign was repeatedly halted by courts, but it has threatened to erode liberty and make life more expensive for families, farmers, and companies.

But the most tangible consequence of the EPA's mission creep has been the neglect of its core functions.

Trump's EPA Administrator Scott Pruitt laid out Obama's legacy in a recent interview with the Washington Examiner. "He left us with more Superfund sites than when he came in," Pruitt said, referring to contaminated lands which the EPA is supposed to be remediating. "He had Gold King and Flint, Michigan," Pruitt went on, referring to the massive 2015 spill of mine waste into the Animas and San Juan Rivers. Obama also left "air quality standards 40 percent of the country in nonattainment," Pruitt added.

The problem? Obama's EPA wouldn't stick to its knitting. Pruitt aptly described the EPA's mindset under Obama: "We think we just ought to re-imagine authority because you know what? We don't know if people are going to pass regulations or states are going to do their jobs."

Pruitt promises to return the EPA to its proper mission and to limit its activities to those actually prescribed by Congress. Will Pruitt's EPA address greenhouse gas emissions? Obama justified his Clean Power Plan by asserting the urgency of the issue. But the executive's belief that an issue is important doesn't give the executive branch the power to address an issue.

The EPA has only the power Congress has given it. Repeatedly, Obama tried to get Congress to pass climate legislation. Repeatedly, he failed. This should have been taken as a sign that there is no democratic will for it. But Obama took these failures exactly the wrong way, deciding that if Congress won't act, he would act on his own.

This is like a soldier deciding that if his officers won't give him permission to shoot, he'll just have to give himself the order to fire.

On climate, Pruitt says the relevant question is "what tools are in the toolbox of this agency to deal with CO2?" Neither Pruitt nor Trump are allowed to put tools in there. Only Congress can. "We're not going to simply just make up our authority," Pruitt said.

Doing exactly what you are called to do by the proper authorities is not a very exciting mission. But such is the lot of conservatism. Executive agencies are role-players, and even the president doesn't get to determine their role. The Constitution is very clear that Congress alone has that power.

We applaud Pruitt's mission of restoring the EPA to its proper shape and size. And we hope he has the humility, the diligence, and the skill to pull it off, for the sake of the Constitution, the economy, and the environment.