[xianshou]

Actually, for several of the presidents, approval + disapproval != constant. For example, Obama moves straight right (up on disapproval) for his first 200 days before descending in approval. There seems to be a substantial difference between the effects of actions that anger some (presumably of the opposing party) and those that disappoint all.

[mbostock]

There's a good analysis of how to design a visualization that shows both approval and disapproval here:

http://eagereyes.org/blog/2012/embracing-uncertainty-two-lin...