DENVER (AP) — From the moment conservative activist and icon Charlie Kirk was felled by an assassin’s bullet, partisans began fighting over which side was to blame. President Donald Trump became the most prominent to do so, tying the attack to “the radical left” before a suspect was even identified.

It was part of a new, grim tradition in a polarized country — trying to pin immediate responsibility for an act of public violence on one of two political sides. As the nation reels from a wave of physical attacks against both Republicans and Democrats, experts warn that the rush to blame sometimes ambiguous and irrational acts on political movements could lead to more conflict.

“What you’re seeing now is exactly how the spiral of violence occurs,” said Robert Pape, a political scientist and director of the Chicago Project on Security and Threats at the University of Chicago.

On Friday, authorities announced they had arrested 22-year-old Tyler Robinson of Washington, Utah, in the shooting. While a registered voter, he was not affiliated with any party and had not voted in the last two general elections. Even so, officials said Robinson had recently grown more political and expressed negative views about Kirk.

There was other initial evidence of Robinson’s potential influences. According to court papers, he carved taunting phrases into his ammunition — including one bullet casing marked with “Hey, fascist! Catch!” — and others from the irony-laden world of memes and online video games.

Nihilistic Violent Extremism is a new FBI category

Experts say political assassins don’t always fall into neatly sorted partisan categories. In some cases, like that of Thomas Mathew Crooks, who shot Trump at a Pennsylvania campaign rally last year, there is little record of any political stances whatsoever. The FBI has said Crooks also had researched then-President Joe Biden as a possible attack target.

Bruce Hoffman, who studies terrorism at Georgetown University, noted that the FBI has created a new category, Nihilistic Violent Extremism, to track the increasing number of attacks that seem to have no clear political motivation.

“Extremism is becoming a salad bowl of ideologies where you can pick whatever you want,” Hoffman said, adding that the increasing number of lone wolf attacks means violence is increasingly unmoored from organizations with clear political goals.

What’s more important than the attackers’ state of mind, experts stressed, is the broader political environment. The more heated the atmosphere, the more likely it’ll lead unstable people to commit violence.

“What they all share is a political ecosystem that’s very permissive about violence towards political rivals,” Arie Perlinger, a professor of security studies at the University of Massachusetts-Lowell, said of recent perpetrators of political violence. “Because politicians are incentivized to use extreme rhetoric and extreme language, that leads to demonization of political rivals.”

Some call for calm, others for ‘war’

That certainly happened after the Kirk killing. The 31-year-old father of two young children was an icon on the new, populist right, especially among young conservatives, and a key ally of Trump. While some conservatives called for calm, others, such as conspiracy theorist Alex Jones and podcaster and former Trump adviser Steve Bannon, called for “war.”

In a speech on the House floor on Thursday, Rep. Mary Miller, an Illinois Republican, said Kirk’s “death was not an isolated tragedy. It is part of a disturbing trend in political violence in our country, encouraged by the radical left and amplified by a corrupt media that has gone from being fake to totally evil.”

Many prominent Democrats issued statements urging calm on both sides. Among them were California Gov. Gavin Newsom and former House Speaker Nancy Pelosi, whose husband was gravely injured by a hammer-wielding attacker who broke into their house in 2022 in an assault that Trump, among other Republicans, mocked.

House Speaker Mike Johnson, a Republican, also called for lowering the temperature across the board.

Trump declares radical leftists ‘the problem’

Still, the most prominent practitioner of polarized attacks remains Trump. Friday morning, shortly after announcing the arrest on Fox News, he said “the radicals on the right oftentimes are radical because they don’t want to see crime. … The radicals on the left are the problem.”

The Anti-Defamation League found that from 2022 through 2024, all of the 61 political killings in the U.S. were committed by right-wing extremists. That changed on the first day of 2025, when a Texas man flying the flag of the Islamic State group killed 14 people by driving his truck through a crowded New Orleans street before being fatally shot by police.

Hoffman said that in modern history, the right has been responsible for more political attacks on people than the left. He said that’s because left-wing radicals are more likely to target property rather than people, and because the extreme right boasts organizations such as militias.

He added that after Trump pardoned more than 1,500 people convicted of crimes during the Jan. 6, 2021, attack on the U.S. Capitol to overturn his election loss, “there’s a belief in certain quarters that, if you engage in violence, the slate can be wiped clean.”

There’s no question there’s also been political violence from the left. In 2017, a 66-year-old man who had supported leftist causes opened fire at a congressional Republican baseball practice, critically wounding Rep. Steve Scalise, who eventually recovered.

In 2022, an armed man angry over a leaked ruling from an coming case that would limit abortion rights tried to enter the home of Supreme Court Justice Brett Kavanaugh. The man backed off when he saw U.S. Marshals guarding the justice’s house, called his sister, and was persuaded to call 911 and surrender to police.

What can take people ‘over the edge’

Pape, of the University of Chicago, said those who engage in political violence are often not the same as the partisans who stoke debates online. He said about 40% of those who perpetrate political violence have a mental illness.

“When there is strong support in the public for political violence, that nudges people over the edge because they think they’re acting in community interest,” he said.

He said he worried about Trump’s one-sided condemnation of left-wing violence, saying it will only inflame the conflict. He compared it to when some liberals condemn all Trump voters as racists.

“The constituents of whoever is doing this, it emboldens them,” Pape said. As for the group being tarnished as uniquely violent, “it creates a bigger sense of defiance,” he added. “What we need to do is convince Trump to do more restraining of his side because we’re really in a tinderbox moment.”