In a stunning move on the heels of the midterm election, President Trump has forced the resignation of Attorney General Jeff Sessions and appointed an outspoken critic of the Mueller investigation — Matthew Whitaker — as acting attorney general, shunting Deputy Attorney General Rod Rosenstein to the sidelines. This raises the specter of a fearful president attempting to muzzle Special Counsel Robert Mueller or hinder him from revealing whether his 18-month-long grand jury investigation has turned up evidence of criminality implicating Donald Trump or his immediate family.

But a 44-year-old “road map” from the Watergate prosecution shows a potential route for Mr. Mueller to send incriminating evidence directly to Congress. The road map was devised in 1974 by the Watergate special prosecutor, Leon Jaworski, with our assistance. We wrote the road map — actually a report — to be conveyed to Congress; it was called “Report and Recommendation” and served as a guide to a collection of grand jury evidence contained in a single document. That evidence included still-secret presidential tape recordings that had been acquired through grand jury subpoena — but which had been withheld from Congress by President Nixon.

The recent decision by Washington’s Federal District Court chief judge, Beryl Howell, to release the document from the National Archives provides a historic legal precedent that could be a vehicle for Mr. Mueller and the grand jury assisting him to share the fruits of their investigation into possible criminal conduct within the Trump presidential campaign and subsequent administration.

In all the discussion about Mr. Mueller’s options when he concludes his investigation, little attention has been paid to the potential role of the grand jury. Chief Judge Howell’s decision unsealing the Watergate road map brings new focus on the role the grand jury might play in the dynamics of the endgame. Although the grand jury is a powerful tool for federal prosecutors, it has historic and independent power and operates under the supervision of the federal judiciary. Following the Oct. 20, 1973, “Saturday Night Massacre” — in which President Nixon forced the Justice Department to fire the original special prosecutor, Archibald Cox — the Watergate grand jury played a critical role in forcing the president to back down, hand over the subpoenaed tapes and appoint a new special prosecutor.