It is taken as an item of faith in certain left-leaning circles that liberals are smarter than conservatives. The most intelligent way to access the claim is to look at data. What are the facts?
There are no IQ tests for voting. Exit polls do ask voters about their educational attainment. I take college degree as a proxy for ‘intelligent’ and use the two major parties as proxies for “liberal” and “conservative”.
Exit poll data from 2010 US House races:
“What was the last grade of school you completed?
Answers for “College Degree”:
Voted For Democrat (D) 47%
Voted For Republican (R) 53% 
This exit poll is consistent with other national elections: those with college degrees are a bit more likely to vote Republican. One can argue, of course, there are some conservative Democrats and liberal Republicans, which would distort the data.
But, it happens the New York Times polled people who hold “more conservative views on a range of issues than Republicans generally. They are also more likely to describe themselves as ‘very conservative’.” This polled group was Tea Party members. “Tea Party supporters are wealthier and more well-educated than the general public”. Of Tea Party members, 23% hold a college degree (vs. 15% of the general population) and 14% hold a post-graduate degree (vs. 10% of all survey respondents). 
Does this prove conservatives are smarter than liberals? Not necessarily. We are using college degree as a proxy for intelligence and one can quibble about the correlation between intelligence and grades. The exit polls do not ask for grades or areas of study which may have different academic admittance standards (e.g. engineering vs. education). But the fact Tea Partiers were more likely to hold a graduate degree certainly argues for good grades and solid undergraduate pedigrees.
Before conservatives turn the tables and declare “I am smarter than you” to liberals, I think there are a number of cautionary take-aways:
(1) There is a bell-shaped curve distribution of intelligence. Most people (of all political views) are in the mid-ranges of the distribution. Any particular liberal, conservative or moderate has a statistical probability of being near the middle of the pack.
(2) Generalized IQ is not the same as being well-informed about any particular issue. An example would be Members of Congress talking about business and economics. 
(3) Being smart and well-informed still does not constitute being right. Examples include 1920s and 1930s Western intellectuals who were smitten with the apparent ‘accomplishments’ of Soviet Communism and fascism in Mussolini’s Italy and Hitler’s Germany. They were dreadfully wrong.
(4) Being smart and well-informed is not the same thing as holding solid judgment. Herbet Hoover and Jimmy Carter were among the brightest of Presidents, but made some very poor decisions.
(5) Intelligent and informed people can look at the same data and come to different conclusions. Try getting Nobel Prize winning economists such as, say, Professors Joseph Stiglitz and Gary Becker to agree on economic policy.
(6) If you are smart but let it go to your head, it might become too easy to be lazy and jump to conclusions or read only periodicals that already support your worldview. I believe truly brilliant people never tire of the pursuit of new knowledge.
(7) “Liberal” and “Conservative” are catch-all terms and people hold all manner of divergent views. For example, libertarians may be said to be economically “conservative” and socially “liberal”.
(8) It is rude and obnoxious to flaunt your IQ, whatever it is. Surely, the golden rule applies!
 “The Employment Policies Institute (EPI) found that only 8.4 percent of lawmakers majored in economics or a related field, while just 13.7 percent studied topics related to business or accounting,” in http://thehill.com/homenews/news/177897-report-three-fourths-of-congress-has-no-education-in-business-economics
Pictures from Wikipedia commons.