I took a moblog photo of a "Republicans for Voldemort" t-shirt, but as I mentioned in that photo description, I really didn't know what it was about. A bit of research on the internet reveals that it comes from a 2003 comic strip called Goats.
So it is a joke. I heartily approve. I still don't know if it's supposed to be a slam on Republicans, California, or just the political process in general, but luckily I don't care anymore. I can just laugh and move along. Ignorance is bliss.