If Barr wants to keep defending Trump, he should take a page from one of his predecessors, Henry Stanbery, who stepped down as attorney general to serve as President Andrew Johnson's impeachment counsel. Stanbery, notably, tried to come back as attorney general after the impeachment proceedings concluded. The Senate did not confirm him.

Some commentators have attacked the special counsel regulations as giving the attorney general the power to close a case against the president, as Mr. Barr did with the obstruction of justice investigation into Donald Trump. But the critics' complaint here is not with the regulations but with the Constitution itself.

When it comes to investigating a president, the special counsel regulations I had the privilege of drafting in 1998-99 say that such inquiries have one ultimate destination: Congress.

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