According to the newly released 2008 National Election Study, approximately 13.5%, up from 12.6% in 2004. A graph from 1952-2008 is below.
This increase may strike some as small, given the total amount of money raised, the emphasis, especially by the Obama campaign, on small donors, and the efficacy of on-line fundraising. (If you include those who gave to other political groups, but not to parties or candidates, the fraction increases to 15.8%, but I do not have handy similar figures for earlier elections.) The caveat is that these numbers are based on the reports of survey respondents, whose memories can be fallible. FEC data may be able to provide corroboration, although federal law does not require campaigns to report donations under $200 (see here).
I also broke down donations across income groups, drawing on the percentiles that have been calculated by the NES over time. This is useful for figuring out who is donating and whether the emphasis on small donors and on-line fundraising has motivated more low- and middle-income individuals to give, thereby counterbalancing the wealthy.
I think the data potentially support competing perspectives. On the one hand, donations are up among almost every group. Those in the lowest income group (0-16%) gave at unprecedented levels in 2004 and 2008. On the other hand, a much larger fraction of the wealthiest 5% also donated in these years (and, presumably, in larger amounts than other groups, on average).
I’m reluctant to generalize about how much “voices” have been equalized in contemporary campaign finance. Both the Pollyannas and the Cassandras are at least a little bit wrong.
More to come from the 2008 NES in the weeks ahead.