What are political affiliations of Homer, Marge, Lisa, Bart and Maggie?

Matt Groening is from Portland Oregon, and while the Simpsons are mostly a-political, they have made the occasional jab at wing-nuts (Bart tells the aliens "Don't forget Ken Starr" when they go to obliterate the humans. I would say centrist-left overall. Lisa screaming liberal, Homer of the nuke plant leans right, Marge is liberal, Bart is purely selfish.