When a mob stormed the U.S. Capitol on Jan. 6, Leslie hoped that this would be her Trump-supporting parents’ wake-up call. She hoped they were watching, maybe feeling ashamed.

Then, a friend called. “Do you know already?” the friend said, and Leslie wondered briefly if someone had died.

The politically liberal 35-year-old cried about the screenshots from her mother’s Facebook page, posts defending the pro-Trump crowds and suggesting that Leslie’s mom made it at least to the Capitol’s steps. Then she reported her mom to the FBI — because “actions,” she said, “should have consequences.”

I think before I realized she was this far gone … there was a sense that perhaps there was some way to reconcile,” said Leslie. “It felt like a death, honestly.”

Some of the flags seen during the Jan. 6 Capitol siege symbolize support for far-right causes, white supremacy and anti-government militias. (The Washington Post)

Leslie shared screenshots of text messages in which she shared her FBI tip “submission complete” page, and another friend recounted hearing that Leslie had reported her mother.

Leslie and many others interviewed for this article spoke on the condition that their full name not be revealed, citing concerns about retaliation or further heightening tensions in their families.

In relationships already strained or severed, last week’s violent spectacle of democracy under siege has pushed some people to take a drastic new step: warning law enforcement. Anguished Americans are turning in friends and family for their alleged involvement in the Capitol riots, contributing to more than 100,000 tips submitted to the FBI and playing a role in at least one high-profile arrest.

For months — sometimes years — the informants say they have watched helplessly as loved ones embraced far-right ideology and latched onto conspiracy theories, from QAnon to viral-video claims of a coronavirusPlandemic.” Extremism has thrived in the Trump era and under pandemic lockdowns, experts say, with more people isolated at home and misinformation rampant online.

“Far-right extremism is not a small-fringe worldview, it’s not an insular cult that only reaches a few dozen or a few hundred people — it’s a wide-ranging worldview embedded in American society,” said Peter Simi, an associate professor of sociology at Chapman University who has studied far-right extremist groups and violence for more than 20 years.

Trump supporters who gathered to protest the certification of Joe Biden as the next U.S. President describe how they view the storming of the Capitol on Jan. 6. (The Washington Post)

Increasingly estranged friends and relatives told The Washington Post they were driven to law enforcement by their own politics, a sense of moral obligation and a fear of what their loved ones could do next.

“They left me no choice because they are on such a destructive path and I do worry about other people’s safety as well as theirs,” said a Texas woman who recounted learning through social media that family members were on the Capitol lawn, apparently beyond the barriers that rioters toppled. Her husband said he can corroborate that she informed the FBI.

Authorities say they have just started making arrests in the wake of the four-hour insurrection attempt at the Capitol, which sent lawmakers into hiding, halted certification of the presidential vote and left five people dead, including a police officer. Hundreds could eventually face charges, and people around the country are volunteering information.

Reddit forums and Twitter threads urge users to turn in even those closest to them — and comfort those who say they did. Some of these online spaces have become safe havens where people share their struggles with the radicalization of a loved one.

“Maybe being held accountable will do them some good,” one Reddit user writes in a thread about reporting Capitol rioters, making sure to include the FBI’s Web form for tips. Elsewhere, someone notes that Ted Kaczynski, the serial terrorist known as the “Unabomber,” was turned in by his brother.

The FBI did not respond to questions about the sources of its Capitol riot tips. But one of their agents described a witness in the case of Larry Rendell Brock, a retired Air Force lieutenant colonel, who called in identifying herself as Brock’s ex-wife. According to the FBI, Brock was photographed last week in the well of the Senate chamber with zip-tie handcuffs — and a military patch recognized by the FBI’s tipster, who explained that she was married to Brock for 18 years.

The Post was unable to reach Brock, his relatives or his public defender.

Some family members have stuck by those arrested, defending them to the media. And for others, contacting the FBI feels drastic.

Waking up from a nap last Wednesday to see the Capitol breach on TV, Robyn Sweet said, she had a feeling that her father, Douglas Sweet, was there. She knew he went to the 2017 “Unite the Right” rally in Charlottesville, she said, and she has listened to him spout QAnon conspiracy theories, speaking of child pedophile rings and a chemical compound supposedly extracted from young captives’ blood.

By the time family located him, Robyn said, her father was already arrested. She says she would not have contacted law enforcement anyway, since she does not believe her father harmed anyone. But she says she has heard from a large community of people who are also mourning their own relatives’ descent into conspiracy — and who say that if they were in her shoes, they would report.

“I have had a lot of people around the world reaching out to me and saying they feel like they’ve lost their parents to this radical Trumpism,” she said. “They feel like they don’t have a family anymore.”

The Post could not reach her father, and it is not clear if he has a lawyer. Posting on Facebook after his arrest, Douglas Sweet dismissed his unlawful-entry charge as the equivalent of a “ticket.”

Simi argued that while right-wing extremism has been building — and ignored — for decades, it has gained greater force during the Trump administration, fomented not only by the president, but other federal officials as well.

This has brought political extremism in America to unprecedented levels, Simi said, adding, “We really are in unchartered territory.”

The coronavirus pandemic has proved a “terrible recipe for extremism,” Simi said. Then came the Capitol riots: “What we saw on the 6th is the culmination of something that has been burning and building for quite some time, and in that sense what happened was quite predictable,” he said.

The Texas woman who says two of her relatives were on the Capitol lawn also described radicalization long in the making.

“They have closed themselves off from the rest of society, everybody else is the enemy,” she said of her relatives. One family member has argued for a “white ethnic state” and the separation of races, she said.

“It’s almost like a cult,” she said. “They all sit around and share conspiracy theories, that the media is lying to them, they don’t want to believe any kind of fact outside of their circle.”

Stunned after learning they were at the Capitol last week, she slept on the issue and then tried to discuss it with other family members. The woman says they brushed her off, echoing claims of widespread voting fraud.

“They said I was being ridiculous and overreacting,” she said. That response helped push her to report to the FBI.

“I felt I had to do something because it seemed like no one else in their immediate circle was going to talk to them,” she said.

Another woman said she informed the FBI about a former friend — estranged because of her increasingly radical politics — who appears in video close to the overrun Capitol, shouting toward police: “Traitor! Traitor Traitor!” The ex-friend, a California attorney named Leigh Dundas, also posted video of herself telling a crowd the day before the Capitol chaos that “we would be well within our rights” to take traitorous Americans “out back and shoot ‘em or hang ‘em.”

The woman shared screenshots of a group chat where she said she reported Dundas to the FBI, and her daughter also corroborated that her mother notified law enforcement.

Dundas did not respond Friday to calls and emails. She wrote on Facebook last week that “the police were the aggressors” on Jan. 6 and blamed “antifa thugs” inside the building. The FBI has said it does not believe antifa was responsible for the day’s violence.

Dundas’s former friend said she initially felt some hesitation about contacting the FBI. But Dundas’s words erased “all of the great things we did together and the wonderful things she did for me,” she said.

“What she said about killing people … she was talking about me.”

Alice Crites and Jenn Abelson contributed to this report.