Charlie Cook is an important pundit. Many insiders listen to him.
Here is an interview with Mr. Cook. The most important part:
"...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."
In other words, if Bush has 48 going into the election, Kerry gets close to 50%. We need to keep working hard--it's our election to win.