US Attorney General Merrick Garland has appointed two special counsels for major investigations the Justice Department is conducting into President Joe Biden and former president Donald Trump.
He tapped Richard Hur to look into Mr Biden's handling of classified documents from his time as vice president in January, after assigning Jack Smith to oversee the department's investigations into Mr Trump in November last year.
An attorney general has the power to assign a special counsel, who acts as a semi-independent investigator on politically sensitive probes, to avoid the appearance of a conflict of interest.
Under US law, a special counsel can be appointed under “extraordinary circumstances”. Historically they have been appointed sparingly, but their employment has become a more consistent tactic in recent years.
During the Trump administration, former FBI director Robert Mueller investigated whether any Americans were involved with Russian interference in the 2016 presidential election.
The operation resulted in more than 30 indictments and several guilty pleas.
Other uses of the special counsel include former president Richard Nixon's Watergate scandal in the 1970s, which eventually led to his resignation from office.
A special counsel was also used during the Iran-Contra affair, which occurred under former president Ronald Reagan, as well as during investigations into Bill Clinton's personal involvement in state-level real estate investments.
Per Justice Department rules, a special counsel must come from outside the government to maintain as much impartiality as possible.
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