"The system we have actually seems to work pretty well," Josh Chafetz, a professor of law at Cornell Law School, said of the return to special prosecutors appointed by the attorney general. "In the few cases where a prosecutor has been fired, the blowback was so intense that a new one was appointed very quickly." [...]

Special counsel Kenneth Starr's investigation of Bill and Hillary Clinton's investment in a real estate entity called the Whitewater Development Company fell squarely into this category. The investigation officially launched in August 1994 to look at Bill Clinton's dealings while he was a state official, and it resulted in charges for a wide range of Clinton associates, including the sitting governor of Arkansas. But Starr then expanded his inquiry to include a probe of White House aide Vince Foster's death (after three years, Starr reaffirmed the conclusion that Foster had committed suicide), claims that the Clintons had fired aides in the presidential travel office to give jobs to their friends (no intentional wrongdoing was found), and an investigation of allegations that Clinton had encouraged Monica Lewinsky to lie about their affair under oath, which ultimately led to Clinton's impeachment.

"It was becoming clear that when you freed the independent counsel from all checks -- political and budgetary -- they could keep expanding their purview kind of indefinitely," Chafetz said. "There was a real sense that he (Starr) had lost perspective of what this investigation was supposed to be for and was pursuing Clinton personally."

With the office of the independent counsel under fire -- even Starr eventually turned on it, calling it "constitutionally dubious" -- Congress chose not to renew it in 1999. The Department of Justice issued regulations instead providing for the appointment of a special prosecutor by the attorney general -- a functional return to the pre-1978 status quo.

Since then, the regulations have been invoked only three times: in 1999, to investigate the FBI's actions in the 1993 raid on the Branch Davidians in Waco, Texas (the special prosecutor criticized the way the raid was handled, but no charges were brought); in 2003, to investigate the leak of undercover CIA agent Valerie Plame's name by the George W. Bush administration (Bush aide I. Lewis "Scooter" Libby, was convicted); and the Russia investigation this year.

Despite Democrats' anxiety, Barrett said he's confident that even if Trump did direct the deputy attorney general to fire Mueller -- an order that Justice Department officials might be unwilling to carry out -- the special prosecutor position wouldn't stay vacant for long.

"Robert Mueller is widely perceived as a competent and credible law enforcement official," Barrett said.