I don't know if it's a sign of decadence exactly. It reminds me of how the Roman Empire tried to reinvigorate its stale religiosity with Christianity (channeling the Mystery Cults that carried on the esoteric insights of the Axial Age). Maybe that's decadence in the sense of boredom with the wealth and power that are taken for granted. Trumpism represents a naïve temptation to conduct a right-wing revolution.

But yes, Trump's success shows the weakness of the liberal institution's mythos. We're disenchanted with liberalism because the economists and politicians oversold the progress in question.