But anyone who is truly worried by these tendencies should fear the consequences of a second Trump administration even more. Anyone who actually cares about academic freedom, or the future of objective reporting, or the ideas behind the statues built to honor American democrats in the country’s public squares, must hope that Trump loses. If he wins a second term, extremism on the left will not be stopped. It will not grow quieter. Instead, extremism will spread, mutate into new forms, and gradually become entrenched in more areas of American life.

Radicalism of all kinds will spread, on the right as well as the left, because America will find itself deeply enmeshed in the same kind of death spiral that the country experienced in the 1850s, a form of negative politics that the British political scientist Roger Eatwell has called “cumulative extremism.” Eatwell described this phenomenon in an article about northern England in 2001, a moment when groups of radicalized white British men physically clashed with groups of radicalized British Muslims. At that time, there were deep economic, religious, and sociological sources for the violence. People in the far right felt themselves to be outside of politics, alienated from the Labour Party that most had once supported. The neighborhoods where both groups lived were poor and getting poorer.

But the mutual anger also acquired its own logic and its own momentum. The perception of anti-Muslim prejudice pushed some Muslims toward radical preachers. The radical preachers provoked an anti-Muslim backlash. Extreme language on one side led to extreme language on the other. Organized violence on one side led to organized violence on the other. Both would blame the other for accelerating the dynamic, but in fact the process of radicalization was mutually reinforcing.