The Justice Department elevated the U.S. attorney in charge of the case, David Weiss, to special prosecutor. Mr. Weiss said in court papers the case “will not resolve short of a trial.” Attorney General Merrick B. Garland on Friday elevated the federal prosecutor investigating President Biden’s son Hunter to the status of special counsel after negotiations to revive a plea agreement on tax and gun charges foundered — a signal that the yearslong inquiry has entered a new and unpredictable stage.