But I talked to four legal experts—two former Justice Department officials, a former White House lawyer and a former U.S. attorney—who all agreed Mr. Trump has the rightful power, as head of the executive branch, to order the FBI to end any investigation.

One expert raised this thought experiment: If President John F. Kennedy had ordered FBI Director J. Edgar Hoover to stop investigating Martin Luther King Jr., would that have constituted obstruction of justice?

It’s also far from clear Mr. Trump ordered anything. His words were vague.