It’s a cognitive bias that’s been well-substantiated by many studies over the decades, nobody has special immunity from it though it can be mitigated. I see both political persuasions being susceptible to it, liberals somewhat more so IMO.
If you want to see a bubble mentality read the posts at the bottom of Nate Silvers blog. They are delusional. I read all of them everyday. No bubble here.
http://fivethirtyeight.blogs.nytimes.com/
Any "cognitive bias" here is well documented which includes the pollsters who Fox News hires:
"(November 1, 2004) Fox News Poll: Kerry 48%, Bush 45% (RV)
Fox News/Opinion Dynamics ^
Posted on Wednesday, October 22, 2008 12:07:57 PM by Chet 99"