John Fund has this at the Wall Street Journal.  Felons for Franken.

Could this be possible?!?: "Academic work by Jeff Manza and Marcus Britton of Northwestern University and Christopher Uggen of the University of Minnesota has shown that a large majority of felons routinely vote Democratic. The two academics estimated that Bill Clinton pulled 86% of the felon vote in 1992 and 93% in 1996. Statistician John Lott's own work in Washington State found that felons were 37% more likely to be registered Democrats even when accounting for race, gender, education level, religious habits, employment, age, and county of residence."