I don't believe that President Bush is a stupid man, but he is clearly simple-minded, inflexible, and ignorant.
Todd Gitlin nicely summarizes Bush's character with regard to intellectual matters:
This is the Bush who was on display in all three debates, the Bush of brute repetition. His sloganeering was, I want to suggest, more than a tactical move to overcome noise. It was more than an advertising method. His rigidity is the shell of his thoughtlessness. Dogma protects him from the perplexity that he finds deeply disturbing. He pumps himself up with bluster. Recycling slogans is only incidentally a stratagem; it is the mind of the man.
There are moments when Bush leaks this truth about himself, a truth to which no witness, friend or foe, has yet mustered contrary evidence. During the second debate, "I'm not telling" was his response when asked whom he had in mind as a Supreme Court nominee in a second term, and followed it up by failing to name his mistakes. One of his more striking statements during four years in office is this remark to Bob Woodward in 2002: "I'm the commander. See, I don't have to explain why I say things. That's the interesting thing about being the president. Maybe somebody needs to explain to me why they say something, but I don't feel like I owe anybody an explanation."
I don't feel like I owe anybody an explanation. Not Paul O'Neill, not Paul Bremer, not Christine Todd Whitman, not Richard Clarke. Not America. Like it or lump it, America. Love me or leave me.
This mental arthritis explains many things about Bush's administration: ignoring warnings that al-Qaeda was planning an attack on the United States, insisting that Saddam Hussein was buddied up with al-Qaeda and building weapons of mass destruction, refusing to plan for postwar Iraq, blowing off budget deficits, declaring that the economy is making splendid progress, piling tax cuts on tax cuts while reasons toss with the wind, closing the administration to press scrutiny.
Karl Rove has been known to say that if you have to explain, you're losing. So he found himself a candidate who wouldn't know how to explain if he wanted to. No wonder he and Bush are a matched pair.
Republicans are right. Character does matter especially a radically flawed one.