IDEOLOGY....Via Matt, here's a Pew chart that shows how the various presidential candidates are viewed by the population at large. What's interesting is that Democrats have almost exactly the same view of the Republican candidates as Republican voters do. Republicans, by contrast, have flatly insane views of the Democratic candidates, placing Obama in Dennis Kucinich territory and Hillary Clinton in some kind of socialist hell netherworld.
There are several theories you could advance for this disconnect. Mine is this: conservative voters are still far more afraid of liberals than liberals are of conservatives. And when it comes to Hillary Clinton, they're just nuts. However, there are plenty of other theories that might account for this too. Feel free to have a go at it in comments.