Street riots, a common occurrence throughout this summer and fall, may well return with a vengeance after the elections.

This year’s organized violence has been managed and directed by radical organizations, and even politicians sympathetic to their goals cannot control them. Just ask Portland Mayor Ted Wheeler, who indulged the street violence wrought by Antifa and BLM for months, only then to be harassed by these groups and challenged for his office from the left.

Groups like Antifa and BLM can turn on progressive leaders as nimbly as they can turn on conservatives because they have neither loyalty nor obligation to any major political party. Buoyed by vast amounts of cash and fellow travelers from other radical organizations, they seek to impose their own ideological agenda, not that of either party.

But the vast majority of Americans are not crazy about political change driven by organized violence. While many embraced marches for racial equality and police reform, popular support for demonstrations noticeably cooled when rioting and looting became more prevalent. While polls over the summer showed many American supported nationwide protests, more recent surveys show a sharp decline. Even progressive politicians have become more reluctant to publicly endorse the protesters most radical demands, such as “defund the police.” Meanwhile, groups leading the protests have tried to soften their messaging, including masking radical demands on their web sites.

While some elected officials and “rogue” prosecutors have effectively countenanced violence on their streets, it is clear that organizations like BLM and Antifa can sustain these operations only where there is a permissive environment.

If there is an eruption of post-election violence, most Americans will likely become even further disillusioned with these tactics. A recent poll, for example, showed most Americans were “fearful” of post-election violence. More violent protests will mean less tolerance for violence as a tool for radical political change.

This raises an important question for the future of public safety. What happens when these mass movements hit a dead end and are unable to move their agenda forward? Some mass movements, such as the 2011 Occupy Movement which purported to lead a “world revolution,” dissipated as a national force. Others, such the Code Pink protests that erupted during the Iraq War, wound up being channeled into more traditional political action such as grassroots and community organizing.

The anti-war and civil rights protests of the 1960s ultimately took a darker path forward. The protests fueled a movement for radical political change, most notably captured by the Students for a Democratic Society. Their strategy, enshrined in the 1962 Port Huron Statement, embraced street violence as a catalyst for change.

Seeking to “bring the war home,” the SDS sponsored four “days of rage” in October 1969. Though bitterly divided over the Vietnam War, Americans proved more interested in resolving their differences through non-violent means. Having badly misread their audience, the SDS eventually disintegrated

However, a hard-core remnant insisted the problem was that their agenda had not been radical enough. They formed splinter groups such as the Weather Underground. Committed to political change through violence, they launched a destructive bombing campaign against government buildings and university ROTC offices and other public targets. It was domestic terrorism pure and simple.

The left’s revolutionary violence was met with counter-revolutionary violence from the right, most notably in the 1995 bombing of the Murrah Office building in Oklahoma City.

It would be tragedy for the U.S. to have endure another wave of domestic terrorism from disgruntled activists, frustrated that they cannot transform America to their liking through peaceful means.

Forestalling this future requires a national consensus to reject violence as an instrument of public protest and political change. To this end, politicians and the media must not only stop normalizing violence, they must declare that rioting, looting and organizing such violent acts are absolutely off the table.

The institutions of civil society also must embrace and foster the message of non-violence. There cannot be any space in the toolkit of legitimate political action for looting, arson, property destruction or arson.

Of course, there will always be a handful of people enthralled with violence. They are criminals and must be treated as such—investigated, charged and punished for their crimes.

The goals is to stop domestic terrorism before innocents are killed and injured, and that must to be done a lawful manner. We can’t repeat past mistakes, like COINTELPRO, where we tried to fight lawbreakers by breaking the law. The cure must not be as bad as the disease.

On the other hand, we can’t constrain legitimate law enforcement activity just because offenders profess political goals shared by those in power. That’s the lesson of places like Portland, where city leaders sympathetic to radical politics allowed terrible crimes to be committed against their own citizens.