Evolutionary biologist Richard Dawkins, asked to comment on Rick Perry disbelief in evolution, went to town on Perry:
Any other organization -- a big corporation, say, or a university, or a learned society - -when seeking a new leader, will go to immense trouble over the choice. The CVs of candidates and their portfolios of relevant experience are meticulously scrutinized, their publications are read by a learned committee, references are taken up and scrupulously discussed, the candidates are subjected to rigorous interviews and vetting procedures. Mistakes are still made, but not through lack of serious effort.
The population of the United States is more than 300 million and it includes some of the best and brightest that the human species has to offer, probably more so than any other country in the world. There is surely something wrong with a system for choosing a leader when, given a pool of such talent and a process that occupies more than a year and consumes billions of dollars, what rises to the top of the heap is George W Bush. Or when the likes of Rick Perry or Michele Bachmann or Sarah Palin can be mentioned as even remote possibilities.
Effective leadership is a complicated thing, and intelligence is only part of it. For instance, there are many, many people just as smart or smarter than Steve Jobs (by some measure of intelligence you could pick) who wouldn't have done half as good a job as he did at building Apple into what it is today. It isn't as though the leaders of Apple's competitors aren't really smart too, but Jobs was consistently better at his job than they were at theirs. Similarly, presidential success involves a lot of different skills, some of which can be developed and some of which are innate, and only some of which are things you can master if you put your big mind to it.
How important we think intelligence is also depends on how we're measuring success. Progressives look at the Iraq war and see a disaster bred in George Bush's intellectual limitations – his disdain for evidence, his reliance on his gut, his inability to see that the world isn't always black and white. Conservatives look at the same events and say, "What disaster?" As far as most of them are concerned, it was a good idea at the time and remains so, so it tells us nothing about the effects of Bush's intellect.
The fact is, however, that Democrats just like their candidates smart. They believe that intelligence is a necessary, if not sufficient, qualification for the presidency. In fact, for many elections now they've been nominating candidates about whom people tended to say, "Man, that guy is smart" their entire lives. The last nominee who didn't produce those reactions was probably Walter Mondale, but it wasn't as though anyone thought Mondale was dumb. Who was the last Republican nominee widely praised for his intellect? Nixon? Moreover Republicans have come to enjoy the fact that their politicians irritate liberals with their anti-intellectualism. So that gives someone like Perry a small but meaningful boost, particularly if he's fighting for the nomination with an obvious smarty-pants like Mitt Romney.