Nate Cohn discounts Gallup's national poll, which shows a tied race:
The poll most likely to scream “headline” is Gallup, which is so far out of line from the other registered voter surveys that I don’t even know what to say about it. Obama leads by about 7 points among registered voters, and, no, the methodological criticisms you’ve heard don’t explain a gap of that magnitude. As Harry Enten of the Guardian (@ForecasterEnten) tweeted today, we would probably blow this off as a clear outlier if it was named something other than Gallup.
But while they have a long history, they haven’t exactly been the most accurate survey in recent years (showing a tied race in 2004 and an 11 point Obama lead in 2008), so there’s just not much cause to assume they’re better than the consensus of other polls, at least that I'm aware of. And Gallup’s case for a tight race was undermined by their traditional partner, Rasmussen, which showed Obama building a 3 point lead once leaners were included. It’s hard to see how Obama could lead by 3 points in a poll weighted to a Republican electorate, but it’s clear that Gallup is completely alone in showing a tied race (at least until Rasmussen returns to showing Romney up 3, or whatever). At the moment, Gallup stands entirely alone. The other trackers, let alone the less regular state and national polls, all show a clear Obama lead at or above post-DNC levels.
Earlier polling crack here.