Does a politician create radical extremists, or could radicalism derive from financial instability, hopelessness, repression, disadvantage, and civil discontent from long-term government failures?

Public discontent from decades of dismal political and socioeconomic policies enabled the space for reactionary leadership. Trump (for example) is a symptom, not the core problem. Would he have gained power if the nation was stable and people felt supported by the government? I doubt it. Trump represented a disenfranchised segment of the population.

There is space for an extremist group in the US, but individuals tend to engage in violent radicalism because US culture creates alienation.

Mass shooters are violent extremists, and violence is prevalent in the US - radicalism has already happened, and the young males (mostly white) are radicals. Maybe we're expecting religious or right-wing zealots and overlook our violent extremists because we're conditioned to.

Violent extremists are a reaction to an environmental situation, and that's not a justification but an explanation. However, I'm interested in other perspectives.