What do you think it is?
First, this is a change election. People are unhappy about the economy and high gas prices. There is a lingering feeling Iraq went wrong.
Hillary is not a change candidate, she's an establishment candidate. She represents the Bush/Clinton dynasty we've had since 1988. And people don't look back on Bill Clinton's years as as a golden age, but as a time of as much division and infighting as at present.
Obama, on the other hand, is a tabula rasa because he's so new and so green. With his gifted oratory and platitudes with few specifics, people can picture their ideal change candidate, or at least liberal Democrats can.
My prediction is that Obamamania will begin to ebb when the Republicans begin to define him as the far left, and in some cases kooky, candidate he is.