Bush’s sloppy speaking style only serves to bolster the perception of his incompetence. That’s why the least discussed but most important theme in the Republican primaries is competence. McCain, Giuliani and Romney are all running as the competence candidates (as would Gingrich, if he jumped in).
Jonah is absolutely right, although I note that Mitt Romney cannot make this argument quite so explicitly. It’s not because he doesn’t have a solid record as a manager; it’s because if a Massachusetts governor were to say “this election isn’t about ideology, it’s about competence” in a Republican primary, every political geek in the world would be doubled over with laughter, trying between giggles to explain the irony to friends.