You've got questions

A comment on my previous post asked about the percent of people rating the parties at 100.  Here is the figure:

There is no clear trend for either.  Although it may not be evident from the figure, there is a positive correlation (about 0.25) between the percent rating each party at 100.  If you add them together to get an index of positive feelings about the parties, you get:

This tracks general confidence in government reasonably well.  It rose in the 1980s, then declined until 1994, then rose into the early 21st century, and then declined.  It was relatively high in 2008, presumably because Obama's nomination increased good feelings about the Democrats.

If you calculate the difference between percent rating the parties at 100 and 0, you get:

So the kind of partisan polarization that has grown isn't a matter of enthusiastic support for one's own party, but dislike or fear of the other party.

Notes:
1.  For this post and the previous post, I used the online data analysis system SDA, which lets anyone do basic analysis of the GSS and ANES.  I have a link to it in the data sources section.
2.  In 2012, Shanto Iyengar, Gaurav Sood, Yphtach Lelkes  published an article entitled "Affect, Not Ideology: A Social Identity Perspective on Polarization," which argued that contemporary partisan polarization was based primarily on feelings of dislike rather than ideology.  I thought it was pretty convincing when I first read it and this analysis has made me more convinced.