Don't take my word for it, there's scholarly evidence from Northwestern University and elsewhere:
Because felons are drawn disproportionately from the ranks of racial minorities and the poor, disenfranchisement laws tend to take more votes from Democratic than from Republican candidates. Analysis shows that felon disenfranchisement played a decisive role in U.S. Senate elections in recent years. Moreover, at least one Republican presidential victory would have been reversed if former felons had been allowed to vote, and at least one Democratic presidential victory would have been jeopardized had contemporary rates of disenfranchisement prevailed during that time.
The above is courtesy of The Sentencing Project, which is not the place to go if you're looking for remedial English lessons, but is if your tastes run to:
Defying One-Person, One-Vote: Prisoners and the "Usual Residence" Principle
Disenfranchisement of Felons: The Modern Day Voting Rights Challenge, Civil Rights Journal
"Free the Vote," Amsterdam News, Ryan Haygood
"Give ex-prisoners a voice," USA Today
"Stripping Ex-Cons of the Right to Vote Should Be a Crime," Chicago Tribune
Jail-Based Voter Registration Campaigns
A timely reminder that prominent Democrat fund raiser, and friend of Bill and Hill, Martha Stewart won't be voting in this year's election. That evil Ashcroft.