A star is born. The big news in the appeals court ruling in the House’s subpoena for President Trump’s tax records is not that the court supports it, though that’s no small thing. It’s the dissent by the newly minted appeals judge on the D.C. Circuit, Neomi Rao. She reckons that the way House is going after Mr. Trump violates the constitutional prohibition against bills of attainder.

Brava, your honor. The chief editorial writer of the Sun has been singing this song since Senator Biden and his Judiciary Committee colleagues launched their attack on Justice-to-be Clarence Thomas. The prohibition on bills of attainder, in which a legislature condemns an individual, are flatly prohibited, both to the state and federal governments. They’re as un-American as titles of nobility.

Judge Rao cuts through the House’s humbug about how this investigation is being made pursuant to the legislative power — as if what the House wants is better laws regulating the president. If that had been its interest, of course, the House would have been trying for generations to pass laws cramping our presidents. The judge gets that the claims to a legislative purpose are gossamer.

The judge quotes a memorandum by the chairman of the House Oversight Committee, Elijah Cummings, a major figure in Congress. The memo, Judge Rao noted, said the committee was investigating “whether the President may have engaged in illegal conduct” and notes that this information would inform “its review of multiple laws and legislative proposals under our jurisdiction.”

What the judge sees in that is the committee announcing “two distinct investigations” — “one to explore allegations of illegal conduct by the President; and another to review multiple laws and legislative proposals within the Committee’s jurisdiction.” Yet, she notes, the committee “justifies both inquiries under the legislative power,” and, she adds, the court’s majority accepts that framework.

She, however, does not. Congress’s legislative powers, she notes, are “limited and enumerated.” In America, “legislative power does not include the exercise of judicial power to determine the guilt or innocence of individuals.” She reminds that the “Constitution prohibits bills of attainder.” And adds that the Bill of Attainder clause was “intended not as a narrow, technical . . . prohibition.”

Rather, Judge Rao quotes case law to suggest that the prohibition of attainder bills was intended “as an implementation of the separation of powers, a general safeguard against legislative exercise of the judicial function, or more simply — trial by legislature.” She reckons the Framers “understood the importance of prohibiting Congress from turning its substantial powers against an individual.”

In respect of the President, there’s only one way the House can go after him personally, Judge Rao reckons — through impeachment. She quotes President Washington himself on this head: “The Constitution contains a single procedure for Congress to address the fitness for office of the President of the United States — impeachment by the House, and subsequent trial by the Senate.”

Judge Rao concludes by suggesting the court majority has crossed a boundary. In other words, that it does matter whether the House really pursuing a formal impeachment. It’s too soon to say whether the case will go to the Nine. It’s not too soon to suggest that the bedrock constitutional question is of a kind which the Supreme Court — and brilliant new appeals judges — were created.