Nearly 3,000 people were killed on 9/11. Today, however, the most urgent threat to Americans’ safety and security comes not from foreign terrorists but from the country’s own citizens. And the threat is aimed at the future of democracy itself.

What makes the threat especially pernicious is that it is not from the fringe but from the mainstream; according to one study, a majority of the arrested Jan. 6 attackers were employed, some of them teachers, chief executives, veterans, doctors and lawyers. They had an average age of around 40. So it’s easy to see why the U.S. government’s traditional counterterrorism infrastructure, built to focus on fringe extremists, is falling short, having foiled only 21 of the 110 known domestic terrorist attacks and plots in 2020, according to the Center for Strategic and International Studies, and failing to prevent the violence and chaos of Jan. 6.

It’s not a stretch to imagine that another Jan. 6 could happen: Amid rampant electoral disinformation, Americans are increasingly prepared to support political violence. Broad swaths of the population refuse to accept the results of a national election, with around only a third of Republicans saying they will trust the results of the 2024 election if their candidate loses. American democratic norms are visibly deteriorating, landing the United States on a global list of “backsliding” democracies in November.

This is why the U.S. government has to stop treating rising political violence and domestic extremism solely as a security problem; otherwise, we will be left with major blind spots in our strategies to combat violent extremism.

In the two decades I’ve been studying extremism, I’ve seen pathways to radicalization change sharply. Throughout much of the 20th century, would-be extremists could really gain access to extremist content only after joining a group — such as the Ku Klux Klan or an unlawful militia organization — with a set ideology, initiation rites and a clear leadership and chain of command. Extremist content had to be sought out.

Today, extremist content is readily available online, in the form of manifestoes, memes, videos and audio that anyone can produce and share. Everyone is just a few clicks away from an ever-expanding series of rabbit holes that offer up whole worlds of disinformation and hate.

Counterextremism tools designed to address threats from fringe groups cannot meaningfully confront the threat from the political mainstream. As violence becomes more spontaneous, less organized and more tied to online radicalization, it is harder to prevent it with strategies that rely on coherent plots and formal group hierarchies.

Because extremist ideas are no longer limited to an isolated, lone-wolf fringe, the United States should focus less on isolating and containing a few bad cells and more on reducing the fertile ground in which anti-democratic and violent extremist ideologies thrive. It needs a public health approach to preventing violent extremism.