The plan in Albany to pass legislation targeting President Trump is a shocking marker of what might be called constitutional nihilism. The idea is to legalize releasing his tax returns to Congress, meaning to the public (please see below). It would violate the spirit of separated powers, the supremacy clause, and the prohibition against bills of attainder, all in a fell swoop.

What prompts this sally is the report in the Times to the effect that state legislators say they have enough votes to pass a bill that would allow the state commissioner of taxation to release the president’s — or anyone’s — state tax return to any one of three congressional committees. The only condition the Times cites is that it would have to relate to a “specified and legitimate legislative purpose.”

Yet every man jack in Albany knows what this is about. It’s about attacking one individual, Mr. Trump. The first clause in the first paragraph in the Times’ story on the scam notes that it takes place amid the “standoff” in Washington over the president’s tax returns. Congress wants to see them, and the executive branch is refusing its request. The showdown could yet end up in court.

It’s the aim of Governor Cuomo and the legislature in Albany to short-circuit the constitutional wrestling match in Washington by moving against the president in the state legislature. Mr. Cuomo knows this is a violation of the prohibition on bills of attainder. Those are bills, resorted to in England and pre-constitutional America, in which legislatures themselves punished individuals.

The prohibition on bills of attainder is laid on Congress in Article 1 of the Constitution. It’s configured against the federal government in the article’s Section 9 and against the states in Section 10. It’s a thicker slab of American bedrock than, say, the rule against suspension of habeas corpus. The Constitution, after all, contains exceptions to the prohibition on suspending habeas corpus.

No exceptions of any kind are countenanced in respect of the prohibition on bills of attainder. They are not allowed, period. Governor Cuomo is trying to skirt this by suggesting he supports the scheme Albany is hatching only “as long as it applies to everybody.” Yet there is no one in the whole Empire State so gullible as to suppose this is intended to be used against everybody.

If it were, the hue and cry would be mind-boggling. Here we are, after all, in a day and age when the world is turning itself inside out over whether, say, Facebook is hawking private data. Here is a bill that, if Mr. Cuomo is believed, is designed to allow the state to hand over private state tax returns to the Congress, meaning — since Congress is a sieve — to everyone.

Wait until the Ways and Means Committee is again in Republican hands. What’s to stop it from requesting Mr. Cuomo’s tax return, just in time for his attempt on the presidency? For that matter, what would stop the Senate, which is currently in Republican hands, from going after Mr. Cuomo’s tax returns? If this is designed to apply only to presidents, that would be another problem.

After all, the Supreme Court has already made it clear that the Constitution doesn’t permit adding to federal offices any qualifications beyond those ordained in the Constitution itself. The famous case involved term limits, but the principle goes beyond that. Once the constitutional conditions are met, that is the end of it in terms of qualification.

In our view, it’s a violation of the spirit of supremacy for a state to butt into a constitutional feud like that which is playing out between an American president and the federal congress. It’s a separation of powers violation for any legislature, state or federal, to try to topple a president through procedures other than the impeachment power. Congress fears doing that, as the Wall Street Journal has well marked, which ought to give the Trump-haters pause.