Hmm... Dunno about him being useful to your political organization, but on a personal level:

I'd say avoidance might be the best policy.. When that phone rings, just don't answer... When he shows up at the house, just don't answer the door; I hate to endorse lying, but if anything comes up, the answer can be "Sorry, dude, I was busy"... "Sorry, I was asleep"... "Sorry, I was away..."

Sooner or later, he'll realize he can't always use you to get around, as a crutch, just simply because you're not there (at least, that's the impression you'll be giving)...

As far as being embarrassed hanging around with him... Dunno there... Maybe you can get him involved in other things or events that go on elsewhere so you won't have to be around him all the time...