AMNA NAWAZ: In the days after the latest indictment of former President Trump, violent rhetoric has been escalating in online forums and in far right militia groups.

This, coupled with heated and combative messaging from Trump and his Republican allies, has extremism -- extremism watchers on high alert.

Following this all of this closely is Jeff Sharlet.

He's a professor at Dartmouth College.

And his new book, "The Undertow: Scenes from a Slow Civil War," chronicles the rise of right-wing extremism over the last decade.

Jeff Sharlet, welcome back to the "NewsHour."

I'd like to ask for your help in translating some of the response we have seen from some Republicans after the indictment of former President Trump, this in particular from a congressman, from Clay Higgins of Louisiana.

If you take a look at this tweet, he said this -- quote -- "President Trump said he has been summoned to appear at the federal courthouse in Miami on Tuesday at 3:00 p.m.

This is a perimeter probe from the oppressors.

Hold; rPOTUS has this.

Buckle up.

1/50K.

Know your bridges.

Rock steady calm.

That is all."

Jeff Sharlet, when you read that, can you help us understand, what is he talking about here and why did it catch your attention?

JEFF SHARLET, Author, "The Undertow: Scenes from a Slow Civil War": Because it's such a specific call to prepare for battle.

A perimeter probe is -- he is saying that the oppressors, by which he means -- he sometimes refers to the cabal or even Leviathan - - Leviathan -- these are QAnon terms for the federal government -- is testing the strength of the real people; rPOTUS, a term he has been using for several years, is the real POTUS.

He believes Trump is the real president.

Buckle up, obviously, he's get ready.

But 1/50K, I had to do some research.

That's one to 50,000, the ratio -- the scale of military-grade maps.

Know your bridges, I was familiar with, is militia-speak for understand the points of attack, literally know the bridges that you can seize and hold and stop federal forces from coming in.

AMNA NAWAZ: Why?

(CROSSTALK) AMNA NAWAZ: Why is it concerning for you to see this kind of language?

How surprising is it to see this kind of language from a sitting member of Congress?

JEFF SHARLET: Well, he's not just a sitting member of Congress.

He has both militia credibility, and he's also been elevated by his party to a chair of the Border Security Subcommittee on the Homeland Security Committee.

He identifies himself as a member of a militia movement called the 3 Percenters.

He first did so publicly, at least, to speaking to a gas lobbyist.

Since then, he's been doubling down.

He's appeared with the Oath Keepers, whose leader, of course, is now serving 18 years.

And even since that tweet, he said there are 3 percent solutions to the indictments.

AMNA NAWAZ: He's not alone and using some of this military or violent references in his language.

We have had a congressman from Arizona, Andy Biggs, who tweeted: "We have now reached a war phase."

The failed Arizona gubernatorial candidate Kari Lake was speaking recently and said: "If you want to get to President Trump, you're going to have to go through me and 75 million Americans like me, and most of us are card-carrying members of the NRA."

Jeff, when you listen to all of this, do you believe there is a real threat of more political violence around Mr. Trump's indictment or really as soon as tomorrow, when he's arraigned?

JEFF SHARLET: My guess is that there's not going to be a January-like event tomorrow in Miami, precisely because so many militia members, a lot had been arrested.

They're afraid of infiltration.

They're afraid of the FBI.

But they have moved to a different kind of action.

I think the other risk is the way that this language insults -- incites those whom we think of as lone wolves, the mass shooters, who, manifesto after manifesto, refer to this kind of political rhetoric and tell each other to go forward, to carry the fight on.

AMNA NAWAZ: Tell me more about that.

From what we know about how this rise of domestic extremism has occurred, it doesn't seem like it takes elaborate planning or a lot of group effort.

As you mentioned, it's often an individual with a set of grievances who is motivated in some way by language like this.

Is that what we're seeing is the trend?

JEFF SHARLET: Yes, although I would question the sort of individual.

When you look at the manifestos of so many of the politically motivated mass killers, they oftentimes cut and paste from the previous one.

They refer to the previous one.

They say that this is part of a long struggle.

They see themselves as soldiers in a war.

And, of course, then you have got other people by General Mike Flynn, who, maybe in mainstream world, is considered ridiculous, but still holds his status as Trump's first national security adviser and as a man we may see in power again if Trump returns, calling for open war.

AMNA NAWAZ: So, what would it take to stamp out this kind of rhetoric?

All of it is being done in defensive and in support of, at this moment, former President Trump.

If he were to come out and unequivocally say, there's no room for political violence in this country, would that end it?

JEFF SHARLET: No.

And, after seven years, are we really expecting that to happen?

Maybe -- maybe now, this is Trump's presidential moment at last.

I don't think it would, though,because the movement goes -- Trumpism is bigger than Trump.

Trump is the avatar, and he's made himself the martyr of the movement.

But the movement, in the minds of men like Clay Higgins, in the minds of those who even see Trump as soft for not going into open combat, is larger than them.

The anger, the anger that Trump invokes -- he's trying to keep up.

In a Saturday night speech, he says: Either they destroy us or we destroy them.

And I don't think he's speaking metaphorically anymore.

AMNA NAWAZ: So, for those who believe in small-D democratic ideals, what's the appropriate way to handle these calls for political violence?

Do we in the media risk amplifying them by covering them at all?

JEFF SHARLET: I think we can't -- we - - look, pretending they're not there isn't going to work.

It's a big part of the American landscape.

What we can do, we can't fact-check a myth.

This is an argument that I made.

We can't fact-check a myth, but we can interpret it.

And we can say, here's what's happening.

And here's how we organize.

The other thing we can do, of course, is support the rule of law.

What's happening in Miami tomorrow is the most important part of this work.

We proceed with the work of democracy.

We proceed with the work of rule of law, and those of us in the press, pay attention, interpret, and call out what it is.

We have got to get away from saying -- this is not conservative rhetoric.

This is -- and I will use the F-word -- this is fascist rhetoric.

This is violent rhetoric.

And we have got to name it as such.

AMNA NAWAZ: That is Jeff Sharlet, professor at Dartmouth College and author of the book "The Undertow: Scenes from a Slow Civil War," joining us tonight.

Thank you for your time.

JEFF SHARLET: Thank you.