The problem isn't one insurrection, it's mass radicalization

What leads to radicalization occurring on that sort of mass scale?

First, you have to have a vulnerable audience receptive to the extremist narrative—individuals who are scared, angry, isolated and looking for answers that satisfy their own personal biases, looking to cast blame for their problems on someone else. They find narratives that tell them their problems are not their fault; it’s the product of a conspiracy trying to undermine your way of life and well-being. Those messages are deeply appealing, because it’s harder to look inside and question your own decision-making and behaviors. Over the past year in particular, we’ve had an unprecedented situation that has left a very large audience receptive to those narratives. The pandemic has left people scared, without jobs and looking for answers to what happens next.

The second thing you need is an influential voice pushing the extremist narrative. And over the past 4½ years, we have had a very influential political leader [President Donald Trump] pushing a narrative that is not only polarizing—not only highlighting that the right and left are far apart on policy issues and disagree on discretionary spending—it’s a narrative of “othering.” It’s a narrative that casts the other side as evil, as “enemies,” as individuals you have to fight at all costs in order to preserve your way of life. We saw this, whether [Trump’s “others”] were Democrats, the news media or the scientific community.

The final thing you need is a mechanism to spread that narrative to the masses.