We may shortly be facing a national crisis. President Donald Trump’s base is egging him on to undertake his own ‘‘Saturday Night Massacre’’ and fire Robert Mueller for committing ... uh, well, for working too hard as a prosecutor.

On Fox News, the host Jeanine Pirro proposed firing Mueller, blaming the Democrats, and imprisoning Hillary Clinton. Speaking of the Mueller investigation, Pirro said, ‘‘It’s time to shut it down, turn the tables, and lock her up.’’

Wow. I’ve reported from tin-pot countries where public figures talk blithely of shutting down prosecutors and imprisoning rivals. I never thought I’d live in one.

Mueller was last known to be a registered Republican and was appointed FBI director by a Republican president, George W. Bush. Newt Gingrich reflected the Republican consensus when he wrote in a May tweet: ‘‘Robert Mueller is superb choice to be special counsel. His reputation is impeccable for honesty and integrity.’’

Yet these days, Gingrich describes Mueller as an ‘‘out-of-control prosecutor’’ guilty of ‘‘grotesque abuse.’’

What changed? Mueller is vigorously investigating whether Trump’s campaign colluded with Moscow, and I believe he has found evidence that it did. We don’t know whether Trump himself colluded, but thanks to Mueller, it seems to me clear that his campaign did.

So Mueller is himself in the cross hairs.

In a July interview with The Times, Trump said that if Mueller investigated the Trump family finances broadly, he reserved the option to fire Mueller. The indictments disclosed Monday do indicate that Mueller is exploring financial transactions, and it’s easy to see why Trump would be sensitive to this. After all, there’s evidence that he and his family played fast and loose with real-estate transactions and tax laws.

‘‘The walls are closing in,’’ The Washington Post quoted a senior Republican as saying. ‘‘Everyone is freaking out.’’ As some conservative voices cheer for Mueller’s ouster, I fear that Trump may replicate the 1973 Saturday Night Massacre and fire Mueller — and presumably a couple of layers of officials in between.

Nixon did this in 1973, firing special prosecutor Archibald Cox and provoking a national bellow of outrage that I remember well, even though I was then a 14-year-old Oregon farm boy. Both houses of Congress were then in opposition hands, providing honest oversight, and the firing of Cox eventually led to Nixon’s ouster.

What’s different this time is that both houses of Congress are controlled by the same party as the president, and I fear that if Trump fired Mueller the result would be less a bellow than a squeak.

The reason for Republican reticence is simple: Trump still has 78 percent backing among Republicans, and senators like Arizona's Jeff Flake who have challenged him have lost support. If you’re a Republican senator, I fear that your political interest may be to respond to Trump firing Mueller by calling for an investigation of Hillary Clinton.

After Nixon fired him, Cox declared: ‘‘Whether ours shall continue to be a government of laws and not of men is now for Congress and ultimately the American people.’’

That is our challenge now, and I hope we can all rise to it, Republicans and Democrats alike. That means not acting as cheerleaders for Mueller’s ouster and for a national crisis. That means insisting that Mueller’s investigation continue, unimpeded by firings or pardons. That means recognizing that there is something larger than party labels, and that is our adherence to laws and the pursuit of truth.

In 1973 we passed the test, and our institutions held; now we may face a similar crisis. It’s time for Congress to wake from its snooze and for citizens to brace themselves not to roll over, but to roar.

Nicholas Kristof writes for The New York Times. Contact him at Facebook.com/Kristof.