Today's Jay Cost post on Clinton and Obama is worth reading. It's long and complicated, but here is Cost's conclusion:
Rudimentary analysis is really all that is valid right now. So, here is mine. Clinton and Obama both have a ton of cash. They both have good messages that could appeal to the Democratic primary electorate. Both of them stand a chance at victory. I would estimate that Clinton has an advantage over Obama that is probably due to her greater name recognition as well the fact that she is a known quantity from a family of proven electoral winners.
If you want to argue that Clinton has an advantage because of the size of her national lead - you are simply on unsolid ground. Recent history has demonstrated quite clearly that these national poll numbers are far from stable. They are subject to sudden, dramatic, and decisive changes because of tiny shifts in the early contests.
Cost points out that, in 2004, Kerry's 6-point victory in Iowa propelled him from a second-tier national poll position to the top of the heap and, eventually, the Democratic party's nomination. There's no guarantee that what happened in 2004 will happen again in 2008, of course. If anything, this election is even more volatile.