From an email sent out by GOP pollster Steve Lombardo:
We averaged the party ID for several national polls over the last several months and found that on average 36% of registered voters claim to be Democrats while only 28% say they align with the Republican party. We conduct dozens of national polls each year and, while our numbers have varied 2-4 points from the above, they have consistently showed a 6-9 point advantage for Democrats. Obama has also closed the long-standing partisan vote gap. National tracking polls show both candidates holding 85-87% of their party’s vote, where in recent years Republicans have enjoyed a 3-5 point advantage. Combine the two, and this is a very difficult hurdle for McCain to overcome. He will need to win independents by at least 15 – 20 points to overcome the party ID deficit. [Emphasis added.]
And yet, as Andrew notes, independents are turning on McCain in breathtaking numbers: in the last seven weeks, his unfavorables among indys have gone from 24 percent to 44 percent.