It's not so much about intelligence...
...as it is about the perceived sense of superiority. Heck, most of the elitists I've named so far are not all that bright. As I pointed out elsewhere, truly superior people are often quiet about it.
If Democrats seem to be overly represented in the "elitist" group, it's because the essence of the Democratic Party philosophy is that nothing will work as it should, nobody will be able to properly run their own lives, and things will just go to hell, unless the Democratic leadership has a very firm grip on the controls at every level of our existence.
It goes without saying that elitists are drawn to this idea more than others are. The idea that "government is best that governs least" is completely alien to them.