I have been active in politics for over 30 years. I have learned many things in that time.
One, people have very short attention spans. This is, in fact, why companies will air commercials repeatedly, because once is not enough for it to sink into peoples' minds. Remember the fake racial attack on the girl in Pittsburgh? Already forgotten by most people. The only ones who will remember it are the shvartsehs and white liberals, but they were not voting for McCain anyway.
There are three categories of voters: those on the right who already had their minds made up for McCain; those on the left who already had their minds made up for Obama, and then the largest group: everyone else in between.
And that larger group (everybody else inbetween), when push comes to shove, votes their pocketbook. That is the bottom line for the masses in the middle.
If McCain will continually hammer away with the Joe the Plumber ads, reminding people that Obama wants to "spread the wealth" (ala Karl Marx), reminds people continually that they will be POORER under Obama's plan, he will win.
Bottom line for most people: their money.