I found this post at Pollster.com really fascinating, particularly this chart:

What's going on here?  One possible lesson is "don't mess around with the health care system".  But the correlation between recent presidencies, and precipitous declines, seems even more obvious.  What changed?

There are two candidates I can think of.  The first is a general rise in partisanship, and decline in respect for institutions like the presidency.  The second is the media. 

The pre-Nixon presidents enjoyed a certain media conspiracy of silence.  They were treated with a fair amount of deference, which is why the public didn't know about FDR's wheelchair, or JFK's affairs.  Post Nixon, they started being a little more aggressive, so approval ratings became more volatile.

One could postulate that Carter, Clinton, Bush I, and Reagan, were all heavily influenced by the old consensus liberal media.  That media had high hopes for Democrats, and didn't much like Republicans.  So all Republicans had to do was, like, not invade Poland, and their approval ratings rose.  The expectations for Carter and Clinton were higher, and therefore their ratings fell.

By Bush II, that consensus had been eroded by the proliferation of niche outlets.  We are now inundated with information about our presidents.  And the more information we have--the more time we spend watching them give bad speeches and make embarassing gaffes--the faster our approval falls.  I suspect that emotionally, we actually prefer that the Great Oz stay behind the curtain, so we could content ourselves with the occasional ceremonial display.  But those days are long gone.

On the other hand, this is all just so much armchair sociology.  Thoughts?