The audience reaction to his statement about 9/11 speaks for itself. I truly think a super majority of liberals believe in the conspiracy theories. Not Pundits or writers or politicians necessarily, but your average guy on the street who describes himself as liberal. And some Air America hosts. It's incredibly embarrassing.
I saw a new poll that shows 27% of Democrats and 40% of Republicans think Saddam was personally involved in 9/11. This is a conspiracy theory of sorts, but based on a shocking level of ignorance. I think the percentage of people who believe in a conspiracy regarding JFK is around 80%. If you take the amount of people who think Saddam was involved--1 in 3--and then add the other theories for that day, I think you'll get a number well over 50% of people who don't believe the official story.