Something funny happened in 2004 where a lot of progressives convinced themselves near the end that John Kerry was likely to win the election even though he was narrowly behind in the polls. Then a lot of people have gone and misremembered that as thinking that Kerry was likely to win because he was ahead in the polls, which he wasn’t. Thus, many are left unable to believe that Obama’s lead in the polls makes his victory likely.
Fortunately, Chris Bowers has a comparison chart we can believe in:
As you can see, Kerry is running well ahead of where Obama was. The theory behind “Kerry’s gonna win” was that undecideds were likely to break heavily for the challenger — heavily enough to make up his small gap in the polls. That wasn’t a crazy thing to believe, but it clearly had a whiff of wishful thinking about it. At the moment, though, Obama just has a big lead.