Charlie Cook Says
As usual, Charlie Cook has some interesting things to say about the election.
On cherry picking polls:
Unrelated to your question, my advice to people is to not pay too much attention to any one poll, there is a temptation to cherry pick, to focus on the one or two polls that tell you what you want to see happen the most, and ignore all others as methodologically flawed. I would look at the averages of polls that are published in various places, an average of many polls is most likely to give you a truer picture than any one.
Real Clear Politics' average of national polls has Bush with a 2.3% lead in a head to head race and a 1.8% lead in a three way matchup.
On undecideds breaking for the challenger:
I cannot remember ever seeing a race where a well-known, well-defined incumbent won a half or more of the undecided vote. Generally it is at least two-thirds to three-quarters going to the challenger, somebody was throwing a figure around of 85 percent, don't know if that is right. But as a general rule, undecided voters overwhelmingly break toward challengers, unless the incumbent is relatively unknown, undefined, appointed or something.
On the incumbent 50% rule:
That's why it is a mistake for people to focus on the spread between the two candidates, the far more relevant figure is the actual vote percentage of the incumbent in a poll (or better, average of polls). If you assume that Nader/others get about two percent of the vote (down from combined 3.1 percent last time), if President Bush is at 46, 47 or maybe 48 percent of the vote going into election day, he probably loses, 49 percent, on the cusp, 50 percent wins.
Real Clear Politics has Bush at 47.8% in both a head to head and three way race.