Special Counsel Can Examine Trump From All Angles

Former FBI Director Robert Mueller’s appointment by the Department of Justice as special counsel on Wednesday puts him in charge of investigating ties between Russia and the Donald Trump campaign. But if history is any guide, that won’t be the most important part of his inquiry. The letter appointing Mueller also authorizes him to examine and prosecute “any matters that arose or may arise directly from the investigation.”

The key words are “any” and “arise” — remember them. Together they confer exceedingly broad authority, more than enough to let Mueller follow his investigation wherever it leads. Don’t forget Ken Starr’s investigation ...