I'm differentiating between identifying with a character and being motivated by that to take a political action and feeling part of a societal group.
But... why? They are so interconnected. You connect to someone, you begin to emulate them in some ways, to think like them about some things, no?

Based on my personal experience, I think that books can definitely do the former but don't do the latter, whereas television can.
That's because your experience doesn't include living in pre-tv times :).