The optimistic portion of my gut tells me that the threat to American democracy represented by Donald Trump and Trumpism has passed its peak and will decline steadily if not quickly. But a grim, smart, “Frontline” documentary, airing Tuesday night, ends with a very smart Republican moderate predicting on camera that such optimism hangs by a slender thread.

Of course, my gut also told me that a racist, incompetent, ignorant greedhead could never get elected in the first place. So I am neither clear nor calm about the threat posed by Trumpism going forward.

Until the last few days (when it plummeted in the aftermath of the violent, Trump-inspired attack on the Capitol), Trump’s approval rating was incredibly stable in the 40-some percent range. Forty-some percent of the electorate is a lot. I’d like to believe that portion is shrinking. But we need some time and maybe quite a bit of time to be sure.

And, for someone like me — who seldom or never heard Donald Trump say anything nor saw him do anything that made me wonder whether maybe he wasn’t as bad as I feared — his 40-some percent approval rating was a reminder that I couldn’t afford to trust my gut about how far lying, stealing, and pandering to racism could get a guy in U.S. politics.

As I struggled to align my hopes and my fears on these points, I had a chance to preview that documentary, which airs at 9 p.m. Tuesday on TPT 2.

It is titled “Trump’s American Carnage,” so you know right away that it has a point of view. And, while I will say that most of what it contains will ring familiar, I think’s an excellent hourlong look back at what our long experiment in self-government has just survived, with plenty of helpful reminders of how it was born and how it grew.

It goes over a few of the lowlights, such as Trump’s famous “fine-people-on-both-sides” reaction to the murderous mob in Charlottesville early in his presidency.

Susan Glasser of the New Yorker says, in the film, that: “Charlottesville was shocking at the time, but actually became the template for much that followed. He understood that there were no practical limits or constraints — except for norms, which he was willing to violate — except for public opprobrium, which he didn’t care about.”

Charlie Sykes, a long-time moderate Republican, an early anti-Trumper, and author of a book called “How the Right Lost Its Mind” says, in the film:

”This was a fight for the soul of the Republican Party, and Trump won.” (Sykes is the moderate Republican I alluded to above.)

During the impeachment crisis over Trump’s extortion effort in Ukraine, Democratic House member Adam Schiff, the prosecutor in that trial, asked Republican senators whether “the daily attacks on the guardrails of our democracy, so relentlessly assailed, have made us numb and blind to the consequences? Does none of that matter anymore, if he’s the president of ‘our party’?”

If Trump gets away with it, Schiff argues, “the danger will never recede. He has done it before; he will do it again. What are the odds, if he is left in office, that he will continue to cheat? I will tell you:  One hundred percent. … If you have found him guilty and do not remove him from office, he will continue trying to cheat in the election until he succeeds.” Reminder: Schiff said that before Trump proved, in recent weeks, how right he was about Trump continuing to try to cheat, but not about the inevitability of Trump succeeding.

The acquittal in the impeachment trial, says Evan Osnos of the New Yorker, “was a kind of permission, and at that point all the guardrails went away. He had nothing to be afraid of. He could do what he wanted.”

The film goes through election night when, after it was clear that Trump had lost, he faced the cameras in front of reporters expecting him to concede, and announced: “This was a fraud. This is an embarrassment to our country,” explaining (lying) two days later that “if you count the legal votes, I easily win.”

Frank Luntz, a Republican pollster but now anti-Trumper, says in the film that Trump supporters who contend that the election was stolen are not lying. “They believe it was stolen,” he says. “They are wrong, but they believe it.”

The next few minutes of the film are about efforts by Trump and his supporters to reject the election outcome, which leads former Sen. Bob Corker of Tennessee — one of the Republicans who decided, early in Trump’s term, that he would rather retire than do what was necessary to be a Republican senator in the Trump era – to say on camera that the refusal of Trump and many millions of his misled supporters to accept the result “demonstrated, to me, the tremendous fragility of our democracy.”

Osnos describes a confrontation between Trump and Mike Pence that lasts hours, in which Pence keeps explaining that his role as vice president to oversee the counting of the electoral votes does not give him any power to transfer states that Biden carried to Trump, and Trump refuses to believe him, accuses him of disloyalty, etc.

But, as you know, after Trump’s Pence plan failed, Trump was down to the last possibility, incite a mob of his supporters to storm the Capitol and prevent the Senate from completing the counting of the electoral vote. Trump told them, falsely, that he would go with them, and then tweeting that Mike Pence had let them down because he “lacked the courage” to do the right thing, which reverberated in the chants of the rioters to “hang Mike Pence.”

The film’s narrator adds: “Four years after Donald Trump arrived in Washington, the country and his party are bitterly divided … over truth, democracy and where we are going.”

Which sets up the quote to which I alluded at the top, from Sykes, who says:

“This is not over. This is an ongoing attack on democracy. The big lie is still out there. This is prologue to what I think is going to be a fixture in American politics for some time. Which is that if lies and conspiracy theories will be embraced by this many people, if one of the two major political parties is not willing to push back against this, it becomes part of the new reality, and we’re going to be living with that for a very, very long time.”

Again, the Frontline film, titled “Trump’s American Carnage,” airs Tuesday at 9 p.m. on Twin Cities PBS, TPT 2.