But it would strike me that this very fact would also be scary for Dem operatives. After all, aside from whatever nuggets are secreted away in her tax returns, Hillary is, at least, a known quantity. She can take a punch with the best of them, and her sheer will to power makes her campaign like the Energizer bunny on steroids (and in a pantsuit, of course). She'll have plenty of money to spend, and a work ethic that just won't stop. Notably, too, she may be able to woo big business in a way the farther-left Obama can't.
On the other hand, some of Barack's behaviors over the past week (most notably the eight question press conference) coupled with coming attractions like the Rezko trial should rightly make a lot of Democrats nervous -- not about what they know, so much, as what it is that they may not know (and, most of all, what they don't know they don't know).
Finally, there's an argument to be made to GOP insiders that now is the time to take on Barack. If he isn't defeated in the general election, he certainly isn't going away. There's one more point worth considering: If Republicans are afraid of beating him now -- when he's still inexperienced, hasn't had time to add "centrist" elements to his record (a la Hillary Clinton) and Republicans are running a candidate with good general election appeal who can credibly carry a reformist message -- would it really be any easier to defeat him after he's gained executive experience and burnished his record with a stint as, say, Governor of Illinois?