If you're under 50 (or simply weren't paying attention the last time a sitting president tried to kneecap a prosecutor investigating that president's possible complicity in an ongoing criminal conspiracy), you might be scratching your head over references to an impending "constitutional crisis" or an historical event called "the Saturday Night Massacre."

But not to worry! As alarming as these phrases sound, both are actually reminders that our country has been here before, and that decisive action by principled public servants may yet rescue us from our current peril.

Ha! Only kidding, young people! We are in deep doo-doo (as one of the incumbent president's predecessors liked to say), and many of our most principled public servants are now in the federal witness protection program.

So the news that President Donald Trump has finally given Jeff Sessions, his chronically abused attorney general, the boot and replaced him with a fellow who seems about as dedicated to the rule of law as Lex Luthor should give you pause, especially if your name is Robert Mueller.

But we really have been here before. And there are some precedents we might want encourage our elected leaders to follow if we hope to emerge from the surreality show called the Trump presidency with some of our most venerable legal traditions intact.

So let's get in the Wayback Machine and revisit the Saturday Night Massacre and the constitutional crisis that wasn't.

Justice Department line of succession

It was October 1973, and another special prosecutor was trying to get his hands on evidence that would ultimately prompt the target of his investigation, President Richard Nixon, to resign.

Nixon might have saved his country another very anxious nine months by handing over the incriminating tape recordings special prosecutor Archibald Cox sought right then and there. Instead, he asked his attorney general, Elliot Richardson, to fire Cox, precipitating some of the most agonized media hand-wringing the country would ever see, at least until 24-hour cable news.

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Richardson, who'd won confirmation by promising senators under oath that he wouldn't interfere with Cox's investigation, resigned rather than carry out Nixon's order. Richardson's No. 2, Deputy AG William Ruckelshaus, confronted the same dilemma and followed his boss's lead. That left his successor, Solicitor General Robert Bork, to give Cox the bad news Bork's bosses had refused to deliver.

For decades after, Richardson and Ruckelshaus were celebrated as heroes who put principle before party, while Bork was condemned as the amoral apparatchik who carried out the order in cold blood.

Only it wasn't quite that simple. Bork did fire Cox, and to this day, practically no one can identify the fourth person in line to become AG if the Justice Department's top three officers get hit by the same truck. (It used to be the U.S. Attorney for the Eastern District of Virginia, but — fun fact — the order of succession can be changed via executive order. Hey, I told you we were in deep doo-doo.)

Give Robert Mueller the Jaworski guarantees

But according to legal ethicists Fred Wertheimer and Norman Eisen, who recounted the Saturday Night Massacre this week in an op-ed for New York Times, Bork was also the fellow who ordained that Leon Jaworski, the special prosecutor Bork appointed to finish Cox's investigation, would retain the independence Cox had been fired for exercising.

A Justice Department order issued on the occasion of Jaworski's hiring specifically prohibited any AG or acting AG from firing the new special counsel just because the president was annoyed with the way he was conducting the Watergate investigation.

It also stipulated 1) that no one in the Justice Department would countermand, or even interfere with, Jaworski's day-to-day management of the investigation; 2) that the Justice Department would not limit the scope of that investigation without consulting both parties' congressional leaders; and 3) that Jaworski would have the right to make his findings public, regardless of whether Nixon or anyone else wanted to keep them confidential.

The credit for all this belongs primarily to Jaworski, who demanded the reassurances he was provided as a condition of taking the job. But it was Bork who signed the order, which allowed Jaworski to persist in pursuing the evidence Cox had sought until the U.S. Supreme Court ordered Nixon to relinquish it.

Matthew Whitaker, the loyalist Trump appointed to replace the unfortunate Jeff Sessions, isn't likely to offer similar assurances to Mueller. But the U.S. Congress could, and the speed with which the president executed the first stage of what could turn out to be his own massacre makes it urgent that lawmakers in both houses do so.

Sen. Lindsey Graham, the South Carolina Republican who has been auditioning for months to be Sessions' permanent successor, has repeatedly pledged to make sure Mueller completes his investigation with no interference from the White House. With Sessions' abrupt dismissal, it's imperative that Graham put some teeth in that promise by sponsoring legislation guaranteeing Mueller the same protections Bork gave Jaworski.

As for a constitutional crisis, Nixon never precipitated one. When the Supreme Court (whose members in 1974 included four justices Nixon had appointed himself) ordered him to turn over the incriminating tapes, the president did.

No one who's been watching Donald Trump for the last two years can predict with confidence whether the current president would comply as obediently with a unanimous ruling from the nation's highest court.

But we'll cross that doo-doo when we come to it.

Brian Dickerson is the editorial page editor of the Free Press, where this column originally appeared. Contact him at bdickerson@freepress.com and follow him on Twitter @BRIANDDICKERSON.