The upper panel plots the proportion of funds raised from donations of $500 or less (including unitemized contributions) against candidate ideology. As is evident, more conservative candidates, particularly those affiliated with the tea party, raise a greater proportion of their funds from small donors. The circle sizes are proportional to the Intrade share prices for the respective candidates as of June 13th. The circles are colored coded based on candidacy status. Those who have officially announced their candidacy are red, those who have not yet announced are purple, and those that have decided not to run are green.
The bottom panel overlays two kernel densities drawn from the 2010 Election cycle. In red is the ideal point distribution of Republican candidates. This gives a sense of how the presidential candidates locate with respect to the party as a whole. In gray is the distribution of Republican donor ideal points, each weighted by the total amount donated during the 2010 Election cycle. This characterizes the fundraising landscape with respect to ideology.
They also contrast their findings with those of Nate Silver. See more at the post.