For extremism researchers, the shooting death this week of a Utah man who was alleged to have made violent threats against President Joe Biden and other public officials highlights a concerning trend. For years, they have watched a steady escalation in violent political rhetoric that appears to be fueling acts of real-life violence.

On Wednesday, the FBI shot and killed Craig Robertson of Provo, Utah as they attempted to arrest him due to his alleged threats ahead of a visit to Utah by Biden. Federal charges against the 75-year-old laid out a history of violent social media posts, not just about the president, but also a range of Democratic politicians and officials, including New York State Attorney General Letitia James, Vice President Kamala Harris, California Gov. Gavin Newsom and Attorney General Merrick Garland.

Robertson has been on the FBI's radar since March, based on a tip from a social media platform, reportedly Truth Social, the company backed by former President Donal Trump. He allegedly posted direct language about his dream to "eradicate" Manhattan District Attorney Alvin Bragg, before Bragg's office indicted Trump.

Many of Robertson's alleged posts contained specific locations, graphic descriptions of imagining watching his targets die and photographs of firearms he appeared to have access to. The word 'assasination' [sic] appears repeatedly and the guns are referred to as "Democrat eradication tools."

Those kinds of details hit a trip wire for federal officials, says Seamus Hughes, a senior researcher at the National Counterterrorism Innovation, Technology and Education Center located at the University of Nebraska, Omaha. Hughes has tracked the number of federal arrests over threats to public officials over the last decade. In 2013, there were 38 such arrests — last year, there were 74. The trend began to escalate within the last five years.

Most FBI interventions are 'a diversion program'

"So a lot of the things we saw in there, you know, they're not that unusual, unfortunately," says Hughes, of Robertson's posting history. What is unusual, says Hughes, is for an interaction with the FBI to end in violence.

"You're talking about hundreds of thousands of tips they get about threats. And many times the FBI will knock on the door, say, 'What are you doing online? Knock it off.' It's basically a diversion program. And those individuals will move on with their lives. The smaller subset, you have to bring up federal charges."

According to the charging documents, Robertson allegedly told FBI agents in an initial visit that his flagged post described a dream, rather than serious intent. He reportedly demanded they not return without a warrant and went on to post that the bureau had "no idea how close your agents came to 'violent eradication.'" Hughes says a significant number of individuals approached by the FBI in these cases say they're unaware their threats violate law. "They just thought it was protected by the First Amendment, which on its face, people understand, that's ridiculous," he says.

Hughes says the rising number of arrests is due to factors including the ease of making public threats via social media, an increased focus from law enforcement on domestic extremism and what Hughes calls a cultural "mood music" that normalizes violent rhetoric.

It's not just federal officials. A recent University of San Diego study surveyed local public officials in that city and found 75% reported receiving threats and harassment. Women, it found, are disproportionately impacted.

Violent political rhetoric is seeping into daily life

It is figures on the political right who are primarily fueling this hostile environment, says Katherine Keneally, a senior researcher at the nonprofit Institute for Strategic Dialogue, although their vitriol isn't just directed against Democrats and public officials.

"What I think is important to note is that Republicans are also being threatened by members of their own party," she says, often due to perceptions of being insufficiently loyal to conservative principles or figures.

Just last week, ISD tracked threats from pro-Trump voices against Florida Gov. Ron DeSantis as he faced criticism for telling New Hampshire voters he was "going to start slitting throats" of "all these deep state people" if elected president.

While threats may target a bipartisan array of public officials, data from the last decade shows that 96% of murders in the U.S. linked political to extremism are committed by right-wing actors. Recent polling suggests, however, that more than half of 2020 Trump voters surveyed believe the opposite is true.

The Salt Lake Tribune has reported Robertson's neighbors, some who had seen his social media posts, broadly characterized him as a harmless, "cranky old guy," who helped community members out with woodworking projects.

The violent language he used has migrated from the fringes of the internet to become a far more common part of daily life, says Keneally, who lives in Montana. "I can go out my front door or hear a conversation and the things that he was posting online, I can hear at a bar, I can hear in line at my grocery store. It is not very uncommon by any means," she says.

Keneally says she tries to promote "vigilance, not panic" about individuals adopting this kind of speech.

"In many ways they don't just wake up one day and say, 'Yeah, the government is coming for me.' That's not what happens. They have had these narratives pushed to them over and over and over again," says Keneally, by far-right media figures who profit from amplifying emotionally resonant narratives about both real and perceived struggles.

As a researcher, Hughes says he worries less for the president, who receives protection from the Secret Service, than for lower-profile public servants.

"The election official in Georgia or the health official in Wisconsin who does not have this apparatus to lean on if they get threats, does not understand how to protect their personal information online, doesn't really know if they want to get into the arena of public debate on these type of things — that's really where my concern is," Hughes says, who emphasizes that even a rising number of arrests for such threats represent a relatively small number compared to the population.

Violent threats against public officials, he says, tend to spike around moments of crisis or major news events.

"So, you know, if we have another event like a COVID or another event like an election, you know, they'll change the targets. You have a subset of people that are angry, that have been told to be angry, and they're focusing their energy on whatever they need to in terms of to show their anger," Hughes says.

Few details about what led up to the FBI shooting Robertson have so far been released, which Hughes says is already helping drive conspiratorial theories about the deadly encounter, comparing it to past federal law enforcement encounters that have ended in violence.

"They're comparing it to Ruby Ridge. They're comparing it to Waco. And it's likely like what we're seeing is that this is just fueling those same narratives that he was concerned about to begin with," he says.