Character.
Peggy Noonan's inciped sop to Regan is entitled, "When Character was King." While I think Regan was a bad president, that's a matter of the policies he pursued. Much as I can decry his policy record, it's undeniable that Regan created a mass consensus in this country. The reason was, for lack of a better term, character.
Howard Dean is the character candidate in this election, and thankfully for us, he's also good on policy.
Howard Dean is the only candidate who can go toe to toe with Bush as the "likable guy" candidate. He's the one who's been best able to connect with the crowds. His straight talk and transparent humanity resonate with people, including (and especially) independents and moderate Republicans uncomfortable with Bush's performance.
Just ask yourself. Is John Kerry more of a "normal guy" than Howard Dean? Is Wes Clark? I know Clark comes from more folksy roots, but his mannerisms are of a General. Not something most people identify with. As a friend of mine in the National Guard remarked ot me, Clark's personality is more a product of military culture than the South.
The remaining Southerner, Edwards, while tremendously likable, suffers all the character problems of Clinton. Clinton, for all this political savvy, was also the Big Dog. Conservative men and women never trusted him. Edwards, while a little less slick and a little more sweet, will seem untrustworthy next to Bush, especially with him hitting so many of Clinton's noted. His demeanor is that of a seducer, a trial lawyer, and people just aren't eager for that right now.
If you watch that damn YEAHHH speech, Dean's a regular frickin' guy getting carried away and having fun with it. My conservative dad can see that, and he appreciates it. He likes how Dean seems frugal, faithful to his wife, and willing to deal with people on a human level.
Combine that with solid moderate/progressive policy and a fighter's unwillingness to take media spin lying down, and you've got the perfect prescription to challange Bush down the streth.
Bill Clinton's Policy + Ronald Regan's Character = Howard Dean