Legal analysts said that as the head of the executive branch, Trump could issue pardons, fire senior officials or order them to shut down investigations. But if his motives were corrupt, such actions could constitute obstruction.

The principle laid out in the letter is “a ludicrous legal theory,” said Neal Katyal, a former acting solicitor general who now works in private practice at Hogan Lovells. “The idea that a president can’t obstruct justice died with King George III, with a brief attempt at revival by Richard Nixon.”