After going quiet in the months before the election, federal authorities are now actively investigating the business dealings of Hunter Biden, a person with knowledge of the probe said. His father, President-elect Joe Biden, is not implicated. Now that the election is over, the investigation is entering a new phase. Federal prosecutors in Delaware, working with the IRS Criminal Investigation agency and the FBI, are taking overt steps such as issuing subpoenas and seeking interviews, the person with knowledge said. Activity in the investigation had gone covert in recent months due to Justice Department guidelines prohibiting overt actions that could...