Some thing fascinating to note about NY Times chart is that Bush owes any of his approval ratings to the country rallying around him after 9/11. His approval was already slipping towards the dark side of 50% when on 9/11, his approval rating spiked. Then it steadily declines until the invasion of Iraq, declines again until Saddam is captured, etc, until now with Kerry (and Senators are notoriously hard to elect) running against him, his popularity hovers around an all-time low. I'm not saying that the administration engineered anything to improve his ratings (I'll leave that for the tin-foil crowd), but this pattern would seem to indicate that the public's thinking about Bush has definitely been clouded by the events of the last four years.
*P.S. I couldn't link directly to the chart, so click over to "Public Opinion: Bush's Term" to see it. The Flash presentation defaults to a map you can manipulate to see which states Bush or Kerry would have to take to win the election. The LA Times offers a similar map. (I think they had theirs first.)