What a cornucopia of constitutional questions will be opened up in federal appeals court at New York tomorrow. That’s when President Trump will get the first hearing in his appeal of a ruling that his tax returns must be handed over in a criminal probe being pursued by the district attorney of New York County. The case is so hot — such a teaching moment — that it’s going to be aired on C-Span.

Pull up a chair, we say. That’s certainly what we’re going to do. Particularly because the liberals are laughing at the president and carrying on about how no one is above the law. The problem there is that the law — the Constitution is a law, after all — doles out a number of immunities. Like the fact that members of congress are privileged from arrest when they are traveling to or from a sitting of the legislature.

Plus, for anything said on the floor of either house, no member of Congress may be questioned in any other place. In everyday lingo, it means that for anything our legislators say at work, they can’t be sued or prosecuted in federal, state, municipal court, or the United Nations. What would an ordinary mortal — a newspaperman, say — give for such dispensation? Is Congress above the law? No, that is the law.

What is so newsworthy about this case — known as Trump v. Vance, the latter being the Manhattan d.a. — is that it represents the first time in the history of America “that a county prosecutor has subjected the President of the United States to criminal process.” That’s the way it’s put in the president’s opening brief. Think of it. For more than 200 years, prosecutors have resisted temptation, until Mr. Vance.

Mr. Trump asserts that the Constitution “prohibits States from subjecting the President of the United States to criminal process while he is in office.” So the issue becomes: “Does a county prosecutor violate that immunity when he issues a grand-jury subpoena, backed by the threat of contempt, for the President’s records, for the purpose of investigating and potentially indicting the President for state crimes?”

America itself has jumped into the case on Mr. Trump’s side. It filed a brief as a friend of the court. The way we read it, America’s concern is not only for Mr. Trump’s position but for the presidency itself. And for the power of the federal courts themselves. This is because Mr. Vance is hiding behind a Supreme Court case, known as Younger, that limited the ability of federal courts to second-guess state courts.

That case was about an effort to use federal courts to cut short the prosecution, by a d.a. named Evelle Younger, of a leftwing teacher named Harris. A lower court halted the prosecution, but the Supreme Court, in a decision written up by Hugo Black, said the federal court couldn’t involve itself in the state prosecution. That became known as the “Younger abstention.”

Both Mr. Trump and America argue that the Younger abstention doesn’t apply in the case of Mr. Trump. It is trumped, so to speak, by constitutional concerns arising from the unique nature of the presidency. Mr. Trump’s brief quotes a famous formulation once written in a law review article by Jay Bybee, who now rides the 9th Circuit: “The President is the only person who is also a branch of government.”

Judge Bybee was saying that all the executive powers in the Constitution are granted to a single individual. A president can hire people — cabinet officers, say — to help him. Unlike a judge or a congressman, though, a president can’t recuse himself, and no one can fill in for him. The United States itself warns that a state criminal prosecution directed at the president risks compromising his powers and duties.

Argument before the 2nd Circuit is likely to go beyond the Younger abstention and the uniqueness of the president’s inherent powers. It’s likely to go to the supremacy clause of the Constitution. That says the Constitution, laws passed by Congress, and treaties are the “supreme law of the land” and bind the judges in every state. The circuit is also likely to fret over one of our favorite cases, McCulloch v. Maryland.

That’s the case in which the Supreme Court blocked Maryland from taxing notes of the Second Bank of the United States. Chief Justice Marshall put the hay down where us mules could get to it by declaring, “the power to tax involves the power to destroy.” To which we would but add: “The power to subpoena tax returns involves the power to destroy — not only President Trump but the Presidency itself.”

What makes this case so intense is that it will affect all future presidents. It comes to a head after a long campaign by the states that cast the losing votes in the Electoral College to foil the President at every turn and use courts from coast to coast to block his efforts to carry out his platform. Tomorrow the arguments will start to come into focus on how far the courts will let this go — or whether the Supreme Court will have to step in.

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Image: Drawing by Elliott Banfield, courtesy of the artist.