To understand the current ‘debate’ about party ID levels in 2012 polls, check out this chart below the fold. You can’t understand what’s going on without it.
I’m not sure this requires a great deal of commentary. You can read it as well as I can.
Two points are worth noting. There is some mild rebound in the number of self-identified Democrats since the mid-point of the Obama presidency, especially recently. And there seems to be some number of moderate Republicans moving to an independent self-identification. But for reasons tied to chart and other data from polls, the decisive move seems to be an exit from the GOP to the right.
Regardless of who’s exiting the GOP and why, I don’t think you can understand this election or the internal make up of the polls without grasping this data.