>they are trying to erase their history of supporting him.

That's not necessarily the case. More likely they just don't want updates anymore.

I don't think any of his supporters are particularly ashamed of supporting him.

Ah, it's been a few years since I logged into Facebook. If a like is analogous to a twitter follow, then this is a lot less interesting than how I was interpreting it.

They could just unsubscribe from his updates, no need to unlike.

But it's also possible that people no longer consider him important enough to be a part of their profile, without actually changing their view of him. People manage to clog up their profiles in a short period of time already, imagine what your FB account might look like in ten years if you never un-like that politician you supported, that band that you loved for a few months, that special edition chocolate bar you couldn't stop buying...

the only real way to make this graph informative is to show it right alongside an obama likes graph.

Not necessarily. You can unlike from newsfeed and Romney has posted a few post-election items.