Over more than four decades, historians and political scientists have parsed almost every aspect of the “Saturday Night Massacre” — from the events that led to the shake-up at the Justice Department on Oct. 20, 1973, to how the decisions made that day would ultimately accelerate the downfall of then-President Richard M. Nixon.

But one mystery remains: Who coined the unforgettable phrase “Saturday Night Massacre,” which remains a part of the political lexicon and was invoked yet again this week when President Trump fired FBI Director James B. Comey. Some say the term is connected to a long-ago birthday party for a Washington Post humor columnist. If true, it would be a wonderful only-in-Washington tale.

But is it?

The “Saturday Night Massacre” refers to Nixon’s attempts that day to order the firing of special prosecutor Archibald Cox, who had been appointed to investigate the president’s role in the Watergate scandal. The two highest-ranking Justice Department officials resigned rather than obey Nixon’s commands. In their view, there was no cause to fire the special prosecutor.

The dramatic events, of course, did all play out on a Saturday — though most of the negotiations broke down throughout the afternoon, rather than at night. And in defying the president, Attorney General Elliott Richardson and Deputy Attorney General William Ruckelshaus lost their jobs.

That said, there were no fatalities, and it certainly wasn’t an actual massacre. So why did the events of Oct. 20, 1973, become known as one — so much so that, nearly a half-century later, the phrase leaps back into use in times of political upheaval?

Early newspaper articles don’t identify the source of the phrase. The news was significant enough to merit six-column-wide headlines on the front pages of The Post and the New York Times the following day. But the word massacre doesn’t appear in any of the initial stories.

The term “Saturday night massacre” first appears in a Post article dated Oct. 22, 1973, in which legendary political reporter David S. Broder describes the high-risk gamble Nixon took in firing Cox (“The Last Roll of the Dice? Nixon Political Clout Shrinks,” read the headline). The now-famous moniker appeared deep in the story, after the jump:

The prevailing White House view was that time is on the side of the President, that as the shock of what is being called the “Saturday night massacre” wears off, the legality and propriety of Mr. Nixon’s actions will be broadly endorsed by Republicans.

Putting aside how spectacularly wrong the White House officials’ prediction would prove to be, the phrasing (“what is being called the ‘Saturday night massacre'”) indicates that Broder probably did not come up with the description first.

“Saturday night massacre” doesn’t first appear in the New York Times until Nov. 10, 1973, about three weeks after the firings, and by that point it seems the Republican Party had adopted the phrase as well:

An atmosphere of concern stemming from that ‘Saturday night massacre,’ as many Republicans now call it, compounded by generally disappointing Republican performances in scattered elections Tuesday, hangs over Monday’s meeting.

Over the next year, however, various media outlets used the phrase with more frequency; gradually, “a Saturday night massacre” evolves into “the Saturday Night Massacre.” By 1974, the Saturday Night Massacre is appearing in Post headlines.

John Dean, former White House counsel to Nixon who testified against the president, said he thinks the phrase may have been uttered on television first. Dean recalled watching NBC that night and hearing reports of the FBI showing up at the prosecutor’s office to shut it down and bar employees from entering.

“That’s when it really got eerie,” he said. It’s possible, he added, that at first the “Saturday night massacre” may have also applied to the chaos that followed at the prosecutor’s office that evening. “I’m pretty sure somebody in television must have thrown it out and that’s where it caught on.”

Available footage of the NBC News report from Oct. 20, 1973, shows anchor John Chancellor describing the situation as “a moment of constitutional drama,” “a totally unprecedented situation” and “a grave and profound crisis.” But “Saturday night massacre” was not mentioned.

Similarly, an ABC News report on Oct. 23, 1973, recapping the chaotic events of the weekend never refers to a massacre.

Gregory Cumming, staff historian for the Richard Nixon Presidential Library, said he has tried to search for the origin but could only conclude “the media” coined the term.

“It was something that the media stuck on the event … to get across the point that this was a dangerous situation,” Cumming said. “Unfortunately, we can’t find that first phraseology. There’s nobody who’s attributed that I’ve been able to find. It’s part of the mythology of the event now.”

Not even Ruckelshaus, the second highest-ranking Justice Department officer who resigned that day, could recall where the phrase originated. In an interview with The Post this week, Ruckelshaus, now 84, did recount how he thinks the story spread so quickly.

In the late afternoon of Oct. 20, 1973, many Washington insiders, including journalists and government officials, were gathered at a birthday party for Art Buchwald, a humor columnist for The Post. It was held at the YMCA in Arlington, Va., which had indoor tennis courts. Buchwald — whom his son would later describe as “a huge social person [but] not a huge exercise person” — thought tennis was the perfect excuse to bring people together to celebrate.

Although Ruckelshaus didn’t attend Buchwald’s party firsthand — “I wasn’t there, obviously,” he deadpanned — he’d heard tales of the gathering over the years, especially what happened once news of the Justice Department had crossed the Potomac River to the Arlington Y.

“It was like somebody dropped a bomb in the middle of this tennis court, and people just scattered to the winds,” Ruckelshaus said. “The press had been so diligent in following the Watergate [scandal] as it ripened that this was a significant event, and it caused them all to leave the party.”

In Ben Bradlee’s 1995 autobiography, “A Good Life: Newspapering and Other Adventures,” the former Post executive editor described the party’s quick unraveling.

“One by one guests were called to the telephone and returned with news about the latest firing,” Bradlee wrote. “Finally the games had to be canceled: too many players rushed back to their offices.”

Bradlee, who died in 2014, was not in attendance at the Buchwald birthday party. He was having dinner at Chez Camille’s, a restaurant near the old Post newsroom.

Sally Quinn, the journalist who would eventually marry Bradlee in 1978, remembers the dinner well because she was there. Bradlee and Buchwald were very close friends, she said in an interview, but they had chosen not to attend the tennis party that year because she and Bradlee were not yet publicly a couple.

“Ben always let people know where he was going to be,” Quinn said. At some point during their meal, Bradlee was called to the restaurant’s phone. Someone from the newsroom was calling with details about what had taken place at the Justice Department, she added.

“He said, ‘Jesus Christ, you’re not going to believe what happened,’ ” Quinn said. “You can’t imagine how shocking it was. It was just stunning.”

Bradlee rushed back to the newsroom and got on the phone with Buchwald, she said, trying to get his best friend to coax information out of various people at his Washington insider-filled birthday party.

“I remember him being in touch with Art, and they were calling each other back and forth at the tennis thing,” Quinn said. “I think Art is the one who came up with the title ‘Saturday Night Massacre’ because he was very funny.”

In subsequent years, Buchwald, who died in 2007, would continue holding his birthday celebration around Oct. 20 (his actual birthday) at the same Arlington YMCA. Only instead of calling it a birthday party, he called it a “Saturday Night Massacre” party.

The humorist’s son, Joel Buchwald, recalled being a teenager at the Arlington YMCA that day, watching his parents host a few dozen guests in the round-robin tournament.

Although he can’t remember how news of the Justice Department firings reached the party’s guests, he said he remembers people’s reactions.

“It was a lot of shock and a lot of phone calls,” he said. “It sucked the air out of the party is what it did.”

As for the phrase “Saturday Night Massacre?” Joel Buchwald can’t be sure whether it was, in fact, his father who coined the term.

“It sounds like something that my dad would have off-the-cuff remarked or quipped,” he said, slowly, pondering the possibility. “It sounds like something he would say, but I can’t with 100 percent certainty say it was him.”

Joel Buchwald paused, then added with a laugh: “But I can with 100 percent certainty say that if no one else claims credit, he would be happy to claim credit.”

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