I have spent nearly 16 years studying how the risk of violence grows in societies around the world and running programs designed to stem the tide. I have seen toxic rhetoric from political leaders result in violence in countries like Iraq and Kenya.

On August 12, the same thing happened in Charlottesville, Virginia. The violent clash there came about in part because of a resonance between President Donald Trump’s language and domestic extremist groups who see a doorway open to their goals – goals most Americans have long thought buried for good.

This homegrown horror represents a potentially greater threat than any we face from foreign terrorist groups. Foreign groups can certainly kill, but they have no power to divide our society. That deeper threat belongs to us alone – but the solution is also in our hands.

Fear and anger make for strong motivation

Let’s consider how the president’s words have encouraged violence.

This quote from Trump, speaking at a rally in West Virginia, predates the angry clash in Charlottesville by just nine days:

“They can’t beat us at the voting booths, so they’re trying to cheat you out of the future and the future that you want. They’re trying to cheat you out of the leadership you want with a fake story that is demeaning to all of us, and most importantly, demeaning to our country and demeaning to our Constitution.”

The counterprotesters in Charlottesville – one of whom was killed – are implicitly among the “they” in this speech.

Fear and anger defined Trump’s candidacy and continue to define his presidency, as in other recent speeches condemning the media, the president’s political opponents, immigrants and the left.

The language Trump uses resembles the language Venezuelan President Nicolas Maduro is currently using to galvanize anti-protest violence, declaring his willingness to take up arms in patriotic terms: “If Venezuela was plunged into chaos and violence and the Bolivarian Revolution destroyed, we would go to combat… We would never give up, and what couldn’t be done with votes, we would do with weapons.” Trump’s language also echoes language right-wing extremist and white supremacist groups use to define the conditions under which violence – toward the government or towards other citizens they see as enemies – becomes legitimate in their worldview.

Trump’s rhetoric doesn’t come out of nowhere. Going back at least to the “southern strategy” in the 1960s, the GOP has spent decades mobilizing fear and anger. As candidates, Republican presidents like George H.W. Bush leveraged fear to secure votes from the white, Christian, male and ideologically extreme demographic to offset the party’s growing distance from an increasingly diverse and progressive American society. Trump’s use of the same tropes is not an aberration, but the culmination of this tactic.

By mirroring extremists’ language, Trump encourages groups already primed for violence by suggesting that the enemy and the situation they have prepared for are present here and now. By refusing to clearly denounce the extremists – and suggesting a moral equivalency between right-wing violence and counterprotesters – he further excuses and reinforces the idea that the right’s violence is defensible, honorable and legitimate.

The patriot paradox

We’ve heard this language from within the “patriot movement” for a long time.

Consider the following words, spoken by Timothy McVeigh in an interview explaining why he bombed the Murrah Building in Oklahoma City, killing 168 people and wounding nearly 700 more.

“Those who betray or subvert the Constitution are guilty of sedition and/or treason, are domestic enemies and should and will be punished accordingly. It also stands to reason that anyone who sympathizes with the enemy or gives aid or comfort to said enemy is likewise guilty. I have sworn to uphold and defend the Constitution against all enemies, foreign and domestic, and I will.”

Every extremist group in history describes its own violence as the legitimate response to a threat that was forced on them. In a South African white supremacist paramilitary training camp, recruits are told “South Africa is bleeding… And this is why we have to train our people to be prepared. There’s millions and millions of blacks around you, smothering you… and killing you… So you have to implement certain systems to survive…” This is the same sentiment reflected in the Rhodesian flag worn by the white supremacist Dylann Roof, convicted of killing nine at an African-American church in South Carolina.

When right-wing extremists and white supremacists view Trump critics, “liberals” and progressive protesters as enemies of the state – and therefore legitimate targets – they feel emboldened to demonstrate more overtly. Indeed, Trump’s anti-elite accusations and claims that the “lying media” is the enemy of the American people hold significantly the same meaning as McVeigh’s words.

American extremist websites exhort the belief that they are defending the Constitution, stopping the theft of the political process from the people and resisting takeover by hostile powers. They draw on the narrative that true Americans are not only able but expected to throw off such oppression.

Even before 20-year-old James Alex Fields drove his car into the crowd on August 12, individual acts of violence linked to racism and extremist American politics were on the increase. In Trump’s presidency, a pattern of increasing hate crimes has continued to grow.

In Charlottesville, white supremacists shouted “Jews will not replace us.” Meanwhile, Eric Trump denounces his father’s critics as “not even people.” They’re the same dehumanizing echoes used to justify levels of violence from cruelty to genocide.

What can be done?

As criticism for Trump’s Charlottesville stance grows, his popularity wanes. The president is becoming increasingly reliant on campaign-style speeches to connect with those who still support him. We must be on guard for the rhetoric of theft and threat, and the implicit call to violence, to intensify.

Many years of experience in dealing with extremism has taught me the threat can be reduced – first and foremost through consistent political involvement by the greatest possible number of people; a strong, united stand against fear and anger; and communication between communities and security providers.

The Department of Homeland Security’s focus on analyzing and countering domestic terrorism, dismantled under Trump, should be rebuilt. The October 2016 strategy for countering violent extremism, which stresses community policing and inclusive governance, should be expanded and improved as a model for cities and states as well as the nation.

Political radicalism isn’t inherently bad. Indeed, the American Revolution wouldn’t have happened without it. The violence perpetrated by domestic radicals, however, cannot be condoned. A former IRA soldier in Northern Ireland once told me of the peace process there, “just because a wave breaks on the beach doesn’t mean the tide isn’t going out.” For Americans horrified at this violence, it’s important to remember that there is no endpoint in politics – only process. What’s wrong now can be changed.

This is an updated version of an article originally published on May 31, 2016.

David Alpher does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond the academic appointment above.