I saw some polling a while back that showed people in their 30s (born in the 1970s) and their teens were more conservative than people in their 20s and 40s. I started wondering if which party was in the presidency during your formative years influences where your political leanings go. It's probably hard to hate the president when you're that age, since you don't understand the issues or the attacks against them, and the president just seems like a father figure that you bond with. So people growing up in the '70s and '90s favor Democrats, while those growing up in the '80s and 2000s favor Republicans. Not by a wide margin or anything, but it seems to be a factor.
Not a big enough factor it seems.