They wouldn’t have gotten far if disdain for comparative bores such as David Miliband or Jeb Bush hadn’t been matched by a fetish for “authentic” jerks. We now have a Western politics in which the center bends toward the fringe, not the other way around.

Nor would they have succeeded if the party faithful hadn’t forgotten, or never learned, why the warmed-over Marxism or dumbed-down nationalism each championed was so thoroughly discredited. Throw in last year’s Brexit vote and Marine Le Pen’s success in reaching the second round in the French election, and the breadth of civic ignorance becomes even clearer.

“As the memory of World War II, the Holocaust and the Gulag fades, so too does the antipathy to the illiberal ideologies that spawned Europe’s past horrors,” writes James Kirchick in his superb if dismaying book “The End of Europe”: “This is evidenced in the rising electoral success of populist authoritarian parties of the extreme left and right, none of which have anything new to say, yet claim the mantle of ideological innovation and moral virtue.”

It took three generations to lose the lessons of prewar isolationism. It took two to ignore the benefits of postwar European integration. If Corbyn’s rise is something to go by, it has taken just a single generation to forget the sins of the far left: anti-Semitism masquerading as anti-Zionism; anti-Americanism masquerading as pacifism; fellow-traveling with dictators and terrorists masquerading as sympathy for the wretched of the earth.

All this is on the voters. It’s easy to come up with reasons for why populists, bigots, radicals, xenophobes, and useful idiots are now in — or edging closer to — power throughout the West. But democracy is a system in which people are only accountable to themselves. The recklessness of their leaders is a result of personal choices at the ballot box, not impersonal social or economic forces.

The news isn’t all bad. Corbyn still fell 64 seats short of a parliamentary majority. Trump’s approval ratings are at 39 percent. Regrets? The Brexiters have a few. And Emmanuel Macron may yet provide evidence that, at least in France, there is gravity, energy, excitement and even sexiness at the political center.

The West hasn’t walked over the ledge, yet. We’re only dancing at the cliff’s edge.