One cannot get an exact number because not every state requires voters to register by party and some do not even allow it.
But, here is some info:
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from
http://www.mysterypollster.com/main/2005/03/realignment_or_.html in 2005
The Pew Research Center survey conducted March 17-21, shows a smaller (but non-significant) shift in the same direction. They currently have Party ID among US adults at 34% Democrat, 30% Republican. The four point edge is slightly higher than in February (32%D-31%R) or compared to their average for 2004 (33%D-30% R) on average throughout 2004.
The Time/SRBI poll conducted March 22-24 showed an eight point Democratic advantage (33%D-26%R), up from a four point advantage measured a week earlier (33%D-29%R March 15-17). The difference, of course, was a statistically insignificant three point drop in Republicans.
The CBS News survey conducted March 28, 2005 showed a five point Democratic edge (32%D-27%R). Although CBS had more independents than usual, the five point Democratic advantage was about the same as on the average of the three surveys conducted with the New York Times in 2005 (35%D-30%R) and the average of all surveys in 2004 (34% D-30% R - click the Complete Results link on the right column of the poll story for full CBS/NYTimes results).
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Here is a Harris Poll from January that says 30 R, 36 D, 22 I (I guess the rest are "some other party")
http://www.harrisinteractive.com/harris_poll/index.asp?PID=630**********************************************************************************
This is from a Washington Post article from 2004:
http://www.washingtonpost.com/wp-dyn/articles/A7329-2004Jun26.htmlSince the waning years of the Reagan administration, or basically since the last periodical cicada mating cycle, the number of "other" voters has proliferated. In the 27 states (plus the District of Columbia) that have been registering voters by party since 1987, the Democratic share has plummeted 8 percentage points, declining from an aggregate total of 51 percent to 43 percent. The Republican share has stayed steady at 33 percent. But the proportion of voters who have not identified themselves with either of the major parties has jumped 8 percentage points, from 16 to 24 percent.
What's impressive about these numbers (at least in the view of political analysts such as me) isn't the phenomenon itself, but its staying power. Myriad polls over the past two decades have shown that voters, when asked to identify themselves politically, divide about one-third Democratic, one-third Republican and one-third independent. But in terms of registration, most have opted for one major party or the other -- perhaps because, in some states, that was the only way they could vote in a party primary. Only recently have registration figures begun to reflect the poll numbers.