The appointment of an outside prosecutor to investigate US president Joe Biden's son Hunter means there are now three special counsel inquiries that could figure prominently in next year's election.
US attorney general Merrick Garland tapped David Weiss on Friday to review whether Hunter Biden violated federal tax and gun laws.
Mr Weiss signalled that he would likely take the president's son to trial.
Earlier, Mr Garland appointed Jack Smith to investigate matters related to president Donald Trump's efforts to cling to power after he lost the 2020 election and classified documents found in the Florida estate where he lives.
Mr Garland also named a special counsel to review classified documents found in Mr Biden's home.
What is a special counsel?
Special counsels are appointed to handle sensitive cases - usually involving political figures or allegations of serious wrongdoing by the government - with more independence than is usually afforded to federal investigators.
Justice Department rules allow the attorney general to appoint one when the department would have a conflict of interest or when he or she decides that it would be in the "public interest" to have an outside lawyer handle an investigation.
The attorney general defines the scope of the investigation, but the special counsel also has the power to investigate new crimes that occur during the probe, such as obstruction of justice.
Unlike other federal prosecutors, special counsels work without day-to-day control by the Justice Department. But the attorney general can still overrule decisions about how - or whether - an investigation should proceed.
What powers do special counsels have?
They have the powers of a federal prosecutor: supervising investigations, deciding whether to bring charges and, if so, taking those cases to trial.
They are required to follow the Justice Department's internal rules, including policies that spell out how to decide whether to bring charges.
They also operate with more public scrutiny. Unlike with other cases, the attorney general must notify Congress if he or she overrules one of the special counsel's decisions. And the special counsel must submit a report laying out the reasons for charging people or declining to do so. Those reports can become public, something that rarely happens in other federal investigations.
Who can be a special counsel?
Usually a special counsel is a lawyer brought in from outside the Justice Department. That was the case with Mr Smith and with Robert Mueller, the former FBI director who investigated allegations that Trump's campaign had conspired with Russia before the 2016 election.
But in some cases, attorneys general have appointed lawyers from within the agency to be special counsels to add heft to investigations they were already supervising.
What is the background of the three special counsels?
Hunter Biden case: Mr Weiss has been the US attorney in Delaware since Mr Trump appointed him to the post in 2018. He was a prosecutor in that office before taking the top job.
Biden Documents case: Robert Hur was the US attorney in Maryland from 2018 to 2021. Mr Trump nominated him for the job. He had been a federal prosecutor in Maryland, worked at Justice Department headquarters and as a partner at a private law firm.
Trump cases: Mr Smith is a former federal prosecutor who led the unit responsible for investigating public corruption. In 2018, he became the chief prosecutor investigating war crimes in the Kosovo War.
How are they different from independent counsels?
After the Watergate scandal, the government handled the most sensitive cases by appointing independent counsels.
Those lawyers worked with an even greater degree of independence than special counsels. The attorney general would seek their appointment, but they would be put in the job by a special panel of federal judges, and those judges could prevent the counsel from being fired.
When statute creating independent counsels expired in 1999 it was replaced by existing Department of Justice rules for appointing special counsels.
