Ideological and rhetorical gauntlets
In other words, if Dean gets the DNC chairmanship, he plans to throw down
the ideological gauntlet.
But Democrats better hope that if he does that during these times when their party has faced power-reducing defections from the center, he doesn't further throw down their party as well.
As against this, Dean is actually relatively moderate. He's a known budget hawk and a muscular multilateralist, for example. While an ideological gauntlet may be thrown down, it's really not an extreme one that will alienate too many people. It's entirely possible that he was selected to throw down a rhetorical and institutional gauntlet, much as the Harry Reid seems to be doing by emphasizing the differences between parties and building political discipline. Following Esmay, Dean is the ideal militant moderate. Ultimately, I don't think these are bad things at all: the Dems have done plenty of soul-searching, and the time has come to pick a path. In keeping with that, my hunch is that Dean was selected as something of a reassuring father-figure, someone that knows exactly what needs to be known. In marketing terms, I suppose one could say that he's a well-defined brand, and can help the Democrats rebrand themselves and become a known quantity.
One of the problems faced by Kerry was that people didn't seem to know what he stood for, and that (stupid) perception has attached to Democrats as a whole; Dean will probably go a ways toward rectifying that image problem.