Since 2004, Rasmussen has polled party ID (Dems versus Reps.) Dems always led, until the fall or 2010. Since then, Republicans have led in all but three months.
Just how big a change did Rasmussen chart? In the last quarter of 2008, the Dems had a 7.8% lead in party ID. Now the GOP has a 1.8% lead, a change of 9.6% in the Republican’s favor. Remember that when you see one of those “polls” that assumes a D-R ID just a couple of points changed from 2008.