What’s a “preference cascade?” In his book, Private Truths, Public Lies, economist Timur Kuran looked at the way “preference falsification” can distort societies, and then collapse suddenly.

The classic example is in a totalitarian society, where everyone has to pretend to love the Great Leader on pain of death. If the authorities manage it right, 99% of the populace can be ready to revolt — but won’t, because each individual thinks he or she is the only one who feels that way. This works until some event suddenly shocks the system, and people realize that they’re not alone. When that happens, things can go south in a hurry. That’s a “preference cascade.”

The United States isn’t a totalitarian society, but media bias has the same sort of effect: By privileging some views and suppressing others, the media give Americans, and itself, a distorted idea of reality. Then, when things crack, it’s a big surprise.

That may be what’s happening here. Obama was presented as unbeatable, and a lot of people believed it — until, suddenly, he looked kind of beatable after all. Once that happened, everything was different.