Archibald Cox, special prosecutor for the Watergate investigation, issued a warning after President Richard Nixon ordered his removal in October 1973. “Whether we shall continue to be a government of laws and not of men is now for Congress and ultimately the American people” to decide, Cox said.

Forty-four years later, the same warning feels appropriate.

The sacking of Cox, known as the Saturday Night Massacre, has been on everybody’s mind following the news that President Donald Trump had fired James Comey ― who, as director of the FBI, was in charge of investigating Russian meddling in the 2016 election and possible collusion with the Trump campaign.

The historical parallels between the removals are not precise. (Historical parallels never are.) But they are close enough to be meaningful ― and they ultimately raise the same question that Cox did, about whether Congress and the public will stand up to a president trying to thwart an investigation of his own administration.

So far, the signs are mixed.

Nixon had a rationale for his decision too

The Saturday Night Massacre was a point of genuine constitutional peril. Months before, a former Nixon aide had revealed the existence of secret White House recordings, raising the possibility that the tapes would provide evidence that senior administration officials ― and even the president himself ― were involved with the Watergate break-in, other crimes, and possible cover-ups.

Nixon’s attorney general, Elliot Richardson, had already appointed Cox, a well-respected law professor and former solicitor general, to serve as independent prosecutor in the case. And Richardson gave Cox special career status in the Justice Department, so that Cox would not be subject to dismissal except for cause ― and could only be fired by the attorney general directly. When existence of the tapes became public, Cox got a subpoena demanding several of them.

Nixon refused, citing executive privilege. Turning over the tapes, he said, would compromise privacy and make it harder for future presidents to get candid advice. Eventually Nixon’s aides worked out a compromise with a Senate committee also investigating Watergate; under the terms of the deal, Nixon would personally prepare transcripts of the tapes ― and then allow John Stennis, a septuagenarian Democratic senator from Mississippi, listen to the tapes to verify that the transcripts were accurate.

When Cox refused to go along, demanding the actual recordings, Nixon ordered Richardson to fire Cox. When Richardson refused and submitted his resignation, Nixon turned to the deputy attorney general, William Ruckelshaus, and the same thing happened. Finally responsibility fell to Robert Bork, the solicitor general, who carried out the president’s instructions. (Memories of that episode would, years later, linger in the memory of senators who rejected President Ronald Reagan’s nomination of Bork to the Supreme Court.)

Both before and after the Saturday Night Massacre, Nixon maintained he was acting out of principle rather than a desire to shield himself from investigation. When imploring Richardson and later Richardson’s deputy to fire Cox, Nixon and his aides went so far as to cite national security, and the possibility that allowing Cox’s insubordination would weaken Nixon’s ability to negotiate with the Soviets.

“Brezhnev wouldn’t understand if I didn’t fire Cox after all this,” Nixon told Richardson in the White House, speaking of Soviet General Secretary Leonid Brezhnev, according to an account in The Final Days by Carl Bernstein and Bob Woodward.

The reaction to the firings was swift and harsh, with Congress reportedly receiving a record number of telegrams and even many Republican members of Congress eventually condemning the move. Some members introduced actual articles of impeachment and soon Nixon had agreed to the appointment of a new special prosecutor, one who eventually helped pry loose the information that led to Nixon’s resignation.

Almost until the end, Nixon maintained his innocence ― famously declaring, less than a month after the Saturday Night Massacre, “I am not a crook.”

Trump could stymie the investigations into his campaign

At this stage of the Russia scandal, it’s not clear that Trump is guilty of anything, or that his actions on Tuesday represent a Nixonian effort to stop an investigation before it produces damning evidence. But the possibility of that certainly exists and it doesn’t take a conspiratorial mindset to think some malfeasance, by Trump or somebody close to him, is likely.

The only way to establish the truth as damning, exculpatory or somewhere in between is to have a thorough, independent investigation. The closest thing to that has been the FBI probe, in no small part because Comey, whatever his shortcomings and missteps, had shown fierce independence.

Trump claims to have a rationale for firing the man investigating him, just like Nixon did. Supposedly it’s Comey’s behavior during the inquiry into Hillary Clinton’s handling of emails ― and instances when Comey deviated from FBI policy. In the abstract, it’s a plausible rationale, just like Nixon’s was. Comey’s actions during the Clinton investigation really did deviate from FBI norms, to the point that plenty of Democrats wanted his ouster.

But Trump cheered those actions in real time, when they were happening. The timing of the firing ― now, rather than in January when Trump took office ― makes the argument laughable. It’s particularly unconvincing because the Justice Department’s own inspector general is already investigating Comey’s handling of the Clinton email investigation. Dismissing Comey now, before the end of that inquiry, makes no sense.

Also there is a New York Times report, originally from Michael Schmidt, that officials at the White House and Justice Department “had been charged with building a case to justify Mr. Comey’s firing since at least last week, and that Attorney General Jeff Sessions had been tasked with coming up with reasons to fire him.”

Politico’s Josh Dawsey filed a similar article, explaining that Trump “had grown enraged by the Russia investigation, two advisers said, frustrated by his inability to control the mushrooming narrative around Russia. He repeatedly asked aides why the Russia investigation wouldn’t disappear and demanded they speak out for him. He would sometimes scream at television clips about the probe, one adviser said.”

Phrases like “constitutional crisis” get thrown around all too easily in cases like these. But the questions this episode raises are really that profound. Is the president trying to subvert the rule of law? Is he doing so to hide evidence that his campaign worked with a foreign government to rig an election?

“There is no question that the President has the legal authority to remove the FBI director,” legal experts Benjamin Wittes and Susan Hennessey wrote at the Lawfare blog. “But there’s also no question that removing the FBI Director in the midst of a high-stakes investigation of Russian influence in the inner circle of the President’s campaign and White House is a horrifying breach of every expectation we have of the relationship between the White House and federal law enforcement.”

A moment of truth for Republicans in Congress

In an appearance on Fox News following the Comey news, Sarah Huckabee Sanders, deputy White House press secretary, said “it’s time to move on” from the Russia investigation ― which is clearly the Trump administration’s hope and quite possibly what will happen unless Congress reacts. With Comey out, the only reliably independent inquiry underway is the Senate Intelligence Committee, and almost nobody believes that panel can do the work as thoroughly ― or operate as free of political constraints ― as an independent prosecutor could.

Senate Minority Leader Charles Schumer (D-N.Y.) is demanding that Deputy Attorney General Rod Rosenstein appoint a special prosecutor ― to take on the role that Cox did 44 years ago, free of political interference. But even with every single Democrat in the Senate backing him, Schumer doesn’t have the leverage to force action, because, unlike 1973, Democrats don’t control either chamber of Congress. They need some Republicans to join them.

A few have already spoken out ― including, critically, Sen. Richard Burr (R-N.C.), who is chairman of the Intelligence Committee. “I am troubled by the timing and reasoning of Director Comey’s termination,” Burr said. “I have found Director Comey to be a public servant of the highest order, and his dismissal further confuses an already difficult investigation by the committee.”

Perhaps the sharpest rebuke came from Sen. Jeff Flake (R-Ariz.), who tweeted the following:

I've spent the last several hours trying to find an acceptable rationale for the timing of Comey's firing. I just can't do it. — Jeff Flake (@JeffFlake) May 10, 2017

But other Republicans were more circumspect and, with the exception of Rep. Justin Amash (Mich.), Republicans have not responded to Comey’s firing with calls for a special prosecutor. That could change in the next day or two or three. Or it might not, in which case Trump could do what Nixon ultimately couldn’t.

A lot is riding on Congress now: its reputation as a co-equal branch, the integrity of law enforcement in America and, just maybe, the ability to fully investigate the role Russia played in the 2016 election.

In 1973, even Republicans came to realize how much was at stake ― not just the guilt or innocence of the president and his advisers, but the constitutional foundations of government. The stakes today appear to be just as high.