The notion is in vogue these days that democracy in America is foundering and that “right-wing extremists” represent the treacherous, hull-splitting rocky shore that looms ahead.

I’m fascinated by this conceit, not least because it is based on the specious ideas that “extremists” can be defined with precision, as with, say, particular types of microbes, and that their heinous goals are equally beyond dispute.

President Joe Biden examined the theme during a Sept. 1 speech at Independence National Historical Park in Philadelphia. He described the conflict as though its parameters were as certain as gravity or some other immutable physical law.

“As I stand here tonight, equality and democracy are under assault,” the president said. “Donald Trump and the MAGA Republicans represent an extremism that threatens the very foundations of our republic. Now, I want to be very clear, very clear up front: Not every Republican, not even the majority of Republicans, are MAGA Republicans. Not every Republican embraces their extreme ideology. I know because I’ve been able to work with these mainstream Republicans.

“But there is no question that the Republican Party today is dominated, driven, and intimidated by Donald Trump and the MAGA Republicans, and that is a threat to this country.”

The inconsistency in those statements is obvious.

If, as the president says, a minority of Republicans are Trump acolytes, then it’s not clear to me why, or how, the GOP is being dominated by them.

Trump’s influence is significant, of course — he is a former president, after all.

Yet it seems to me that Biden is hedging — he’s eager to brand Trump’s supporters as enemies of America but unwilling to tar a majority of GOP voters, with midterm elections looming, with the same brush.

It’s not the flimsy logic that bothers me — it was a partisan speech, after all, and thus short on nuance — but rather Biden’s insistence that his political opponents seek to demolish America’s fundamental principles.

Republicans want to win elections, certainly.

But this is quite a different matter than their threatening, to borrow Biden’s words, “the very foundations of our republic.”

The president in his Sept. 1 speech went on to say: “And here, in my view, is what is true: MAGA Republicans do not respect the Constitution. They do not believe in the rule of law. They do not recognize the will of the people. “

Here again the accusations are so broad that they’re all but meaningless.

MAGA Republicans respect nothing in the Constitution, nor any laws? Not even the Second Amendment? Not even rulings by the U.S. Supreme Court?

This is transparently silly.

The president is on more solid ground with his reference to “the will of the people” — he later spoke in more detail about Republicans refusing to accept the results of the 2020 presidential election.

Yet some Democrats were similarly skeptical of the 2016 election, and their conspiracy theories about Russian meddling are no more persuasive than the GOP’s claims about widespread election fraud four years later.

The Jan. 6, 2021, riot at the U.S. Capitol was deplorable.

But it didn’t prevent Biden from being inaugurated. Indeed it had no chance of doing so.

Biden’s speech annoyed me, but mainly because it was insulting in its implication that Americans would blithely believe that political foes — even ones as obnoxious as Trump — are determined not merely to win elections but to replace our republic with some dystopian authoritarian regime.

I was, however, much more disappointed by a recent column written by documentary filmmakers Ken Burns — the most renowned current practitioner — Lynn Novick and Sarah Botstein. Their film, “The U.S. and the Holocaust,” premieres Sept. 18.

I have higher standards for documentarians than for politicians.

Although their op-ed replicates Biden’s theme — the phrase “our democracy itself under attack” shows up in just the second paragraph — the filmmakers indulge in comparisons that Biden had the decency, or at least the good sense, to eschew.

They summoned the Nazis from the moldy old graves where we’re best to leave them except for lessons about true evil.

Hitler and the Third Reich must always remain a prominent episode in world history, one we must never forget. And I have no doubt that the new documentary will be fascinating and well-crafted.

But I think it is inappropriate to imply that there is any parallel between America’s political climate today and Germany of the 1930s and 1940s.

This misguided association manages to both slander current Americans and deflect responsibility from Hitler, which is no small rhetorical trick, though I’m sure this was not the filmmakers’ intention.

They contend that while researching their documentary they “were not looking for parallels to the present, though we knew they were there, even before Donald Trump came to office. But now these dark moments in our history echo all too clearly.”

The gist of their argument is that some Americans in the 1920s and 1930s, by championing noxious theories such as eugenics, and supporting racism and restrictions on immigration, inspired Hitler and the Nazis.

“Germans could look to the U.S. not as a counter-model, but as a societal prototype that embraced racism and exclusion,” the trio of filmmakers wrote.

The historical record supports the basic validity of that statement.

Yet the difference between Germany and the U.S., both in the interwar period and during World War II itself, is so dramatic and so indisputable that to imply any connection, much less one that persists nearly a century later, is both absurd and offensive.

Any rational, intelligent person understands that the Holocaust is a unique, and uniquely terrible, episode, and one for which Hitler and his henchmen are solely responsible.

Their guilt is not diminished an iota because some bigoted Americans, including such prominent citizens as Henry Ford and Charles Lindbergh, believed ludicrous things about race, or because indefensible policies such as Jim Crow laws persisted even as American soldiers, some of them Black, were fighting, and dying, to stop the Nazis.

Yet I find it more galling still that the filmmakers would imply that a significant number of Americans in the third decade of the 21st century would welcome a revival of the awful and ill-conceived beliefs, and government policies, that stain our nation’s history.

Curiously, in their op-ed they contend that these “dark moments in our history” — which they absolutely were — today “echo all too clearly.”

Yet an echo, of course, no matter how clear, is still a transient sound, one that diminishes rather than grows in power over time.

I don’t believe that echoes from nearly a century ago threaten America’s foundation, or that today’s political tussles, no matter how amplified by social media, are anything but a slightly more bitter version of the same old unpleasant recipes that must always be available to sample in a free society.

I trust that our country is made of better stuff, and that my fellow citizens can detect the foul flavor of promises that have poisoned other places and which, fortunately, proved fatal to those whose aims are not merely objectionable but are outright evil.