Washington ? If President Trump fires Special Counsel Robert S. Mueller III, that won’t necessarily be the end of his investigation. Power to continue the probe, and report on its findings, could also rest with Beryl Howell, who as chief judge of the federal district court here oversees the Mueller grand jury.

To prepare for the crisis that Mueller’s firing would cause, Howell should review plans made by John J. Sirica, her predecessor as chief judge, to deal with the firing of special prosecutor Watergate Archibald Cox in October 1973. Sirica intended to install a new special counsel to complete the work of two Watergate grand juries.

Sirica recalled his deliberations in his 1979 memoir, “To Set the Record Straight.” After President Nixon ordered Cox’s dismissal in the famous “Saturday Night Massacre,” Sirica wrote, “my first concern was that the grand juries be protected.” He summoned the jurors three days after the firing and admonished them: “These two grand juries will continue to function and pursue their work. … You must steadily and deliberately pursue your investigations.”

But who would present evidence once Cox was gone? Sirica had an answer to that, too. He would appoint the new special counsel, acting on his authority as chief judge. He rebuffed an intervention by public-interest lawyer John F. Banzhaf III seeking to reverse Cox’s firing, and made a bold affirmation of his judicial power:

“If the court [meaning Sirica] decides it is necessary to appoint special counsel, the court doesn’t feel it needs guidance or service from outside organizations. If this time comes, the court will select someone to represent the grand jury.” He summoned Henry Ruth, the senior member of Cox’s staff, and told him and several assistants: “The law can take care of this situation.”

To be sure, various objections could be made to the Sirica stratagem. He was positing a judicial power that some (but not all) constitutional scholars would question as a violation of the constitutional separation of powers. And Mueller, unlike Cox, has used the grand jury sparingly — to ratify evidence rather than as an investigative tool. That’s probably because so much of the evidence in Mueller’s counter-intelligence probe has been classified.

But the Watergate case offers a fascinating alternative approach to protecting Mueller’s investigation, through the judiciary rather than Congress. “Just as with Sirica, it’s improbable that the chief judge of the district court will sit idly by and watch the president corrupt the system,” argues Robert Muse, a prominent defense lawyer and former member of the Senate Watergate Committee, who pointed me to Sirica’s memoirs.

Howell seems especially unlikely to tolerate disrespect for Mueller’s investigation. Before she was appointed chief judge by President Obama in 2010, she prosecuted money laundering, public corruption and narcotics cases as an assistant U.S. attorney, and she was later general counsel of a firm specializing in cybersecurity and digital forensics. She also served as general counsel for Sen. Patrick Leahy, D-Vt., when he chaired the Senate Judiciary Committee.

The judicial branch’s power to appoint prosecutors is clearly established in cases involving contempt of court, argues Peter Shane, a professor of constitutional law at Ohio State University. He cites Rule 42 of the Federal Rules of Criminal Procedure, which specifies that in contempt cases, if the government refuses to prosecute, “the court must appoint another attorney to prosecute the contempt.”

“The judicial appointment and supervision of prosecuting attorneys was not uncommon in state courts in the early Republic,” Shane adds. “Grand juries are part of the judiciary, and the judicial appointment of a prosecutor to protect the integrity of a grand jury process would not violate the separation of powers.”

Courts also have clear power to allow reports by grand juries. The Fifth Circuit found in a 1973 ruling: “There is persuasive authority and considerable historical data to support a holding that federal grand juries have authority to issue reports which do not indict for crime, in addition to their authority to indict.” The U.S. Attorney’s Manual notes that this “power to issue reports” exists in common law.

The judicial approach to protecting Mueller may be preferable to the congressional alternative of trying to shield the special counsel through legislation. Such legislative efforts could backfire if Trump’s supporters succeeded in defeating the intended protective measure — further emboldening Trump.

Sirica put it simply when he told the grand jurors in 1973 that their work wasn’t over even though Cox had been fired: Carrying on with the “sacred and secret” investigation was “an obligation of citizenship which it fell your lot to bear.”

— David Ignatius is a columnist for Washington Post Writers Group.