The magic number is 50%. In the last 40 years, a president who is at 50% or higher on January 1st of the election year has won re-election. Those under 50% on that date, have lost. Period.
Bush is anywhere from 49 to 58% now. He needs to shore up his numbers by the end of the year. This is important for several reasons. First, fundraising. People stop giving money if they think it will be a waste. Secondly, the inevitability factor. People like backing a winner. You would be amazed at some in the mushy middle who will vote where they think most people are, because they like being on the winning side, and it doesn't really matter to them too much which side they are supporting. Thirdly, media coverage. The media are fear mongers, hype mongers, and pack animals. If the president appears unbeatable, they keep repeating that. If they sense weakness, they pound on him, and ignore the opposition's weakness. They are hyenas. Literally.
If I could ask you, are you concerned with Bush having alienated many conservatives? I have only anecdotal evidence for that but the sample is telling: many people here on FR state they'd not vote for Bush.