Reading the Early Voting Tea Leaves
You'll want to read Molly Ball's examination of early voting in the swing states. Here's a bit that should convince you to read the whole thing:
The blizzard of numbers, of claims and counterclaims, can be so daunting it's tempting to just throw up your hands and decide there's no truth to be had, just spin. But an objective analysis of early turnout can provide valuable tea leaves for Election Day. In many states, election officials disclose how many Democrats and Republicans have voted thus far. We don't know who they're voting for, but in most states, this alignment is a good proxy for the candidates. (Then there's the mystery of those voters who aren't affiliated with a party. In polls, independent voters have generally favored Romney, leading his campaign to claim an edge in this category, but for the purposes of analyzing early voting it's impossible to tell.) It's important to consider which party has historically had the early vote advantage -- Democrats, in most states -- and whether early voting makes up a substantial amount of the vote, which varies from state to state. ...
This analysis isn't conclusive; it's a faint clue at best. But with as much as 40 percent of the nationwide vote likely to have been cast before the polls open on Tuesday, here's what the early vote is telling us so far.