In that case, American politics has been dominated by radicalism at least since the time we let one of our own vessels blowing up due to lax maintenance drag us into the Spanish-American War, if not longer. Politics is usually more about feelings than facts. The rational voter is a myth. We don't imagine Americans were mulling the issue of slavery by reading the great thinkers of the day in an era when 1 in 10 white men couldn't read, do we?
There have been radicalism popping up here or there, but it only dominates the politics some of the time. Usually, politics is about real details, not great abstract and non-negotiable things.
And yeah, interesting that you put slavery here. The way the US handled it wasn't through democratic institutions. (You have a famous saying about how those institutions fail from time to time and people must help them die.)
