The General Social Survey gave people a vocabulary test (often considered a very rough proxy for education and intelligence) called Wordsum and also asked people for their political affiliation. Wordsum is scored from 0 to 10, with those scores corresponding roughly to normal scores (note that I calculated this by using percentiles from the data, so the percentiles should be seen as being with respect to the people who were surveyed, and not the population at large. There are probably some people left out of the survey for some reason or another):

0 - lower than 62
1 - 62 - bottom 1%
2 - 70 - bottom 3%
3 - 76 - bottom 6%
4 - 82 - bottom 12%
5 - 89 - bottom 23%
6 - 96 - bottom 40%
7 - 104 - top 40%
8 - 110 - top 24%
9 - 116 - top 14%
10 - 123 - top 6%

Below I have the data graphed out (the scale is a little cut off, light blue means moderate Republican, pink means strong republican, and brown means independent). I personally think that the results are fascinating.

1. Political affiliation does not correlate very strongly with vocabulary. I calculated a coefficient of 0.111 (where 1 is a perfect correlation, and 0 is no relationship).

2. Democrats seem to dominate the very top and most of the bottom of the distribution. Republicans tend to be in the upper middle sections.

3. Third party affiliations correlate very well with vocabulary. It's likely that people who are uneducated (and have small vocabularies) don't study politics as much, and therefore don't seriously consider third parties.

4. Independents tend to dominate the bottom of the distribution. This is probably because independents lose out on participating in the primary, and uneducated people don't realize that this is the case. It's also possible that uneducated people feel so disenfranchised with the system that they are unwilling to endorse a political party.