I need to know how many registered Democrats there are of all
registered voters in the United States. This may seem like an easy
question to answer! I've been searching all afternoon on the internet
& haven't come up with anything usable. I could use some help.

Hello.

From USA Today:

'An estimated 201.5 million U.S. citizens age 18 or over will be
eligible to vote Nov. 2, although many are not now registered. Of
these, about 55 million are registered Republicans. About 72 million
registered Democrats.
About 42 million are registered as independents, under some other
minor party or with a "No Party" designation.'
source: USA Today
http://www.usatoday.com/news/opinion/columnist/neuharth/2004-01-22-neuharth_x.htm

Thus, the USA Today figures indicate that of the approximately 169
million registered voters, 72 million (or 42.6%) are registered as
Democrats.

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search strategy:
"million registered democrats"

I hope this helps.

Perfect. Thank you!