In answer to your questions, we know who the sponsors of MoveOn.org are. The lamestream media are hiding that info because they are bigots for the left.
McCain came up with this stupid scheme because he wanted "to make his mark on national policy" and he's incapable of thinking the subject to its logical conclusions.
My understanding is that these organizations are NOT tax-deductible.
Congressman Billybob
Latest column, "Says the Wuss: Ma, He's Touching Me"
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Disclaimer: I am NOT an expert :)
But, it is my understanding that PACs, 527s and 501 (c) (4)s are tax exempt, meaning they do not pay income tax like a regular corporation would. And donations to them are NOT tax deductible to the donor.
A 501 (c) 3 organization, on the other hand, is tax exempt just like the others, but donations ARE tax deductible to the donor (eg: American Heart Assoc, etc.).
As you might expect, it is harder to get a c3 approved by the IRS than the others.