Other investigations took significantly longer than Mueller’s to result in charges. It took more than a year for the independent counsel investigating potential mismanagement and corruption by Samuel Pierce, Ronald Reagan’s secretary of housing and urban development, to issue charges (Pierce was never indicted, but lower-level staff were convicted). The same was true of investigations into whether Clinton’s HUD secretary, Henry Cisneros, had lied to FBI agents about payments to his former mistress and whether Clinton’s secretary of agriculture, Mike Espy, had improperly taken gifts from businesses and lobbyists (Cisneros pleaded guilty to lying to the FBI and was later pardoned by Clinton; Espy was acquitted at trial).

Some investigations are especially lengthy because special prosecutors often stumble on other information when they’re pursuing a case, Harriger said. It’s unlikely that Mueller’s investigation will follow the same path as the Whitewater probe, in which Kenneth Starr’s review of Bill and Hillary Clinton’s investment in an Arkansas real estate company during Bill Clinton’s time as a state official blossomed into several unrelated investigations, including an inquiry into the death of White House aide Vince Foster and, ultimately, the scandal related to Monica Lewinsky and the president’s impeachment. But it’s too early to know for sure where Mueller will go.