Bush is clearly not the most articulate politician around, but that is one thing. The notion that Kerry had a heads up on the debate questions is not an impossible thing to consider. Despite Jim Leherer's initial comments, I simply do not trust journalists. Anyone who does is simply not paying attention to reality.
Kerry basically admitted he had the questions ahead of time. He said something to the effect of he won't finish up discussing a point he was making---he will 'wait until the homeland security question which is coming up later in the debate.' (Paraphrased)