Benjamin Zimmer at Language Log has erased any last doubts about Bush on Democrat iclessness, here – he's continuing to use 'Democrat' (adj.) freely, if not consistently. As to whether it's carelessness or malice, it at the least shows that he doesn't care enough fix it. And he's clearly paying attention to what he said and how he said it, given the situation.
He knows that this is a very negative term and we usually are able to control our use of such language. I remember reading that when he served on corporate boards, he was criticized for not contributing anything except "jokes, usually off color" (or words to that effect). So, hey, maybe he wasn't doing that on purpose either ... maybe it's some bizarre form of coprolalia.
For what it's worth, I only saw excerpts from Bush's performance, but he looked and sounded like he was doing his overarticulation thing a few times, like not flapping the /t/ in center. He does stumble pretty often, as always. (You can listen to the NPR recording of the conference here.) If time permits (don't bet on it), I'll have a listen and post a followup.