NEW YORK SUN: Attainting Trump.

By suggesting criminal charges could be in the cards for President Trump, the House committee investigating the events of January 6 isn’t just weakening their case before the Supreme Court. They’re also skating close to the constitutional prohibition on bills of attainder. That’s one of the limits Americans placed on Congress, enjoining what the Supreme Court has called “trial by legislature” — exactly what the January 6 committee appears eager to conduct.

The Constitution forbids bills of attainder as “a general safeguard against legislative exercise of the judicial function,” Chief Justice Warren explained in United States v. Brown. Under the British monarchy, such bills were used to punish without a trial individuals accused of disloyalty, treason, or any conduct the parliament found objectionable. The Framers, Chief Justice Warren wrote, “sought to guard against such dangers by limiting legislatures to the task of rule-making.”

Members of the January 6 committee seem to have lost sight of that wisdom. So far, they’ve been racking up victories in their effort, in federal court, to breach Mr. Trump’s executive privilege. The Supreme Court, though, has yet to decide whether to hear Mr. Trump’s appeal asking to shield his papers. It strikes us that the committee’s chairman has handed Mr. Trump’s lawyers valuable ammunition of Congress’s intent.

It’s an abuse of legislative power, that — like the dual frivolous impeachments of Trump based on bogus evidence — sets a precedent for more abuses in the future.