Rasmussen's sample is D+3
http://washingtonexaminer.com/rasmussen-yes-dems-likely-have-2-4-point-advantage-in-november/article/2509409#.UGeycRj2Ez6
“Republicans have ranged from 32 to 37 percent. Right now, our sample looks like 36 percent Republican versus 39 percent Democrat.”
In this particular sample I calculated that in order for Obama to be at 48% and Romney at 44% and based on the internal data of the poll provided by profit_guy in post # 5 then there is 40% democrats, 31% Republicans, 29% Independents...