“Kerry Cascade”

So why does Senator Kerry keep winning primaries despite the fact that most voters don’t know very much about him or like him all that much?
Duncan Watts takes a shot at it, citing Solomon Arsch’s experiments in “social decision-making.” Simply put, Asch might argue that voters are picking Kerry because prior voters selected Kerry, and then they rationalize their decision with “electability” or some other nonsense. The results from this are mixed:

In many situations, social decision-making isn’t a bad idea at all. After all, the world is a complicated place, and other people often do have information that we lack. So, we can often do reasonably well, or at least no worse than the people we are copying, by letting them do the hard work for us.
But sometimes the people we are copying aren’t working either, and that’s where the problems come in. When everyone is looking to someone else for an opinion�trying, for example, to pick the Democratic candidate they think everyone else will pick�it’s possible that whatever information other people might have gets lost, and instead we get a cascade of imitation that, like a stampeding herd, can start for no apparent reason and subsequently go in any direction with equal likelihood. Stock market bubbles and cultural fads are the examples that most people associate with cascades, because they are generally accepted to represent “irrational” behavior (although, curiously, not to the people who are participating in them�just ask a teenager why she wants to get her navel pierced; she won’t say “because it’s a fad”), but the same dynamics can show up even in the serious business of Democratic primaries.

I hope I’m wrong about this, but I fear the latter variant is at work here. Because the Kerry cascade sure seems irrational to me.