Scott Olson/Getty Images

Florida voters lead the pack in early voting this election cycle, as nearly 60 percent of the more than 900,000 early ballots have been cast in the Sunshine State.

While early voting is unlikely to attract many swing voters, it can help turn out the party faithful. That's an especially urgent need for Democrats, who historically struggle more than the GOP with voter participation during midterm elections. And as more states add early voting options, the difference can add up: Three out of ten voters in the 2010 midterms cast an early vote.

Republicans in several states have introduced measures to limit or do away with early voting, an unpopular move that only 11 percent of Americans support.