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Washington's late night

It could be a late night in Washington state tonight -- or more likely, a long week. That's because Washington is one of two states (Oregon is the other) that conducts its elections via a mail-in ballot.

Ballots arrived in mailboxes about two weeks ago, and voters have until 8:00 pm local time tonight to postmark their ballots or turn them in at "drop off" centers around the state. According to Washington's Secretary of State's office, more than 40% of voters will have voted before the 8:00 pm deadline tonight. But that still leaves the majority of ballots that won't be counted until AFTER Election Day.

Sen. Patty Murray (D) and her challenger, former state Sen. Dino Rossi (R), are preparing for a prolonged count. Both campaigns tell NBC they don't expect know the winner until at least Thursday, so don't expect any concession speeches tonight from either candidate unless it's a complete blowout. But that seems unlikely -- the latest polls have Murray ahead by just a handful of points, well within the margin of error.

The reality is that hundreds of thousands of ballots won't even arrive in counting centers until midweek. The biggest county, King County (Seattle area), says it takes 48 hours to process ballots before they can even be tallied. And both state parties are gearing up for a fight -- they've retained attorneys who specialize in recounts, including the seven-month dispute in 2004 of Rossi's razor-thin gubernatorial loss, and the nine-month recount of Sen. Al Franken's win in Minnesota.

The only county that is not exclusively vote by mail is Pierce County, the state's second largest, which encompasses Tacoma and its southern suburbs. Pierce is Washington's second largest county, and its full of swing independent voters who will decide this election. Voters in Pierce county can vote at the polls on Election Day, so both parties will be watching election results there closely. If Republicans are winning Pierce County late tonight, the Rossi team will be celebrating.

On the campaign trail last week, Rossi was calling his race the "51st seat" -- meaning that if things break the Republicans way, the nation might be watching the results in Washington to determine who controls the Senate. If that's the case, we could be watching for quite a few days before we know the answer.