Early Voting = End of Election Day Exit Polls?

Through Sullivan, I see the Washington Post is reporting that "more than 60 percent of those across the country who have taken advantage of early voting are registered as Democrats." This, despite the fact that registered Democrats make up only a little more than 30% of the electorate, with Republicans a bit below that, with most of the remaining unregistered, Independent, or other party affiliations. [If somebody has better numbers than this on registration, lemme know.]

Set aside whether the 60% number is exactly right for the moment. Suppose that, in early voting, Democrats simply make up a much larger percentage than their share of the electorate overall. This makes sense to me, as those who are excited by the possibility of the first African-American president would want to get out and make sure their votes are counted. Democrats have an advantage in enthusiasm according to just about every poll that has been out there this cycle.

But doesn't this also mean that we're in for a long night on November 5? If Democrats have voted early, they're not around the voting booth on Election Day to be asked by pollsters who they voted for. Therefore, while they would be overrepresented now, when nobody's around to ask them, they'll be underrepresented on 11/5. What might that mean for the kind of election night coverage we've come to expect, when networks "call" the states before the votes have been counted? Remember, when CNN or whoever "calls" a state for one candidate or another, they're not doing it based on counted votes, but on overwhelming exit poll numbers.

A prediction: Just as last cycle saw exit poll numbers favorable enough to John Kerry that websites like Slate showed a smiling Kerry, suggesting that the super-secret-yet-somewhat-leaked poll numbers were putting Kerry ahead of Bush, the exit polls will be way off. All day long, cable news will be teasing that maybe McCain unexpectedly has closed the gap, maybe the Bradley Effect was real, maybe Obama couldn't seal the deal, whatever, because all the exit polls will show McCain's share overrepresented. In the end, we truly won't know until all the actual votes get counted, rather than what will by then be obviously unreliable exit polls.

Bottom line: whether it ends up being close or not, don't expect to know who's president before you go to bed on the night of November 5th (or the morning of the 6th).