Judge Neomi Rao was an engaged and active questioner on the bench Friday as she made her debut as a newly minted jurist on Washington's federal appeals court.

The former Trump administration regulatory czar sat upright and occasionally leaned forward during her first sitting, appearing with a laptop and a binder of papers. Rao was appointed to the U.S. Court of Appeals for the D.C. Circuit by President Donald Trump and confirmed in March, filling the vacancy left behind by Brett Kavanaugh's elevation to the U.S. Supreme Court.

Rao, along with Judges David Tatel and Sri Srinivasan, heard arguments in two appeals. The first related to a criminal re-sentencing case, and the second was a challenge to the Environmental Protection Agency's decision in April 2018 to no longer enforce part of an Obama-era regulation that limited the use of hydrofluorocarbons, a powerful greenhouse gas.

The attorneys for an environmental group and states challenging the EPA argued Friday that the agency's decision amounted to a final agency action, which would require providing notice and time for public comment before its implementation. Lawyers for the agency and intervenor Mexichem Fluor contended it was interim guidance. They said the agency's move was based on its interpretation of a D.C. Circuit ruling in 2017 that invalidated a different part of the Obama-era rule.

As the panel grappled with how “final” the EPA's move was, Rao pointed out that court precedent guides judges to look also at the language of agency guidance itself. She asked Peter DeMarco, a lawyer for the Natural Resources Defense Council, what he made of the EPA's wording in its April 2018 document, which said it was providing guidance “in the near-term.” DeMarco argued those words didn't “defeat” the finality of the agency's move itself.

Rao had questions for Justice Department lawyers, too, who represented the EPA and fielded tough questioning from Tatel and Srinivasan. Rao asked Benjamin Carlisle if it was the EPA's “view” that the D.C. Circuit's ruling in 2017 had effectively invalidated the entirety of the previous agency's policy or if the agency was taking the position that, given the ambiguities in the ruling, it was simply offering its interpretation in the interim. Carlisle replied it was both.

Rao's first question came in USA v. Mark Smith, where a man is appealing a district judge's denial to reconsider his sentence. The original sentence for Smith, who was convicted on drug distribution charges, was based on a guideline range that the sentencing commission later reduced. Sandra Roland, an assistant public defender, argued Friday that the trial court committed “procedural error” in declining to reconsider his sentence.

Rao only asked one question, after both Tatel and Srinivisan weighed in, asking Roland if she was suggesting that any sentence above the guideline range would be unreasonable. Roland said she believed it was unreasonable in this case, though not in all instances.

Before arguments began, Tatel offered brief introductory remarks, welcomed his “newest colleague” to the bench and wished her a “long and successful” tenure.