"These donors are successful because they do not let principle interfere with their political donations." -- University of Virginia political scientist Larry Sabato, referring to donors who support both Democrats and Republicans.
Among other things, the above quote points to why the support of Wall Street for President Obama in 2008 exists but is easily overblown, and also points to one major reason why (besides
Citizens United) a shift to GOP donations in 2010's midterm elections is also overblown in significance - especially if it is being used as alleged evidence of support for specific GOP or Tea Party candidates.
It also shows that political donations for entities or persons that support both parties financially can not reasonably be called "political speech" when it is actually the purchase of access or an attempt to pacify a contribution requester from being offended by a denial.
(For an article discussing the shift containing the above quote, see
http://www.chron.com/disp/story.mpl/metropolitan/7187927.html )