What to Watch For

But Pennsylvania in particular is the one to watch. If Barack Obama holds onto Pennsylvania—the only state where John McCain seems to have been closing the gap over the last week of the campaign—then winning virtually any red state (Virginia, Florida, Ohio, Colorado, Missouri) would probably clinch the election for him.

9 PM EST. Polls close in Colorado, New Mexico, Wisconsin and Minnesota.

Wisconsin and Minnesota should be called fairly quickly for Obama; if they aren't, that's a sign that something has gone truly wrong for the Democratic ticket. New Mexico looks like a safe Obama-state too, but since its vote-counting is notoriously slow, it may take longer to call. The key number to watch in Minnesota should be the difference between Obama's margin of victory and Al Franken's tally in his Senate race against Norm Coleman. If Franken is staying within 5-7 points of Obama as the vote begins to roll in—say, for example, Franken leads by 2 while Obama leads by 7—then Obama's coattails should carry Franken into the Senate. If not, the race may be Norm Coleman's to lose.

Colorado, meanwhile, is the last of what I'd characterize as this year's "Big Three" states (the others are Pennsylvania and Virginia). If Pennsylvania and Virginia have split their votes (and Obama hasn't picked up Ohio or Florida), then Obama probably wins if he wins Colorado, and loses if he doesn't.

10 PM EST. Polls close in Nevada, Iowa, Montana and New York.

This is the earliest point at which the race might be officially called for Barack Obama—there just aren't enough electoral votes out there, even if he's swept every swing state, to get him to 270 until New York's 31 come in. But assuming that we don't know the outcome of the election by this time, Nevada, where Obama has expanded his lead and where much of the state has already voted, could be Obama's ace in the hole—possibly offsetting a loss in Pennsylvania if paired with other pickups like Colorado and Virginia. The key area to watch in Nevada is Washoe County (Reno), which John Kerry lost by 4 points in 2004 but where the Obama campaign has registered thousands of new voters. If Obama wins Washoe, that means the state—and probably the country—is his.

11 PM EST. Polls close in California, Oregon and Washington.

None of these states are in play in the presidential contest this year. The status of the race, however, could have a potential impact on California's Proposition 8, which seeks to strike down same-sex marriage. If Obama appears as though he's headed toward a landslide victory, crestfallen conservatives might not bother heading for the polls to vote for Prop 8.

Finally, even if the presidential race has been called by that point, Democrats looking for a little schadenfreude may want to stay up late until the midnight poll close in Alaska, where Ted Stevens is almost certain to be bounced from his Senate seat by Democratic challenger Mark Begich. Should the Democrats pull out an upset in Georgia or Kentucky, it may be Stevens' seat that gets them over the top to a 60-man majority.

Nate Silver is the creator of FiveThirtyEight.com, a popular political blog.

© 2008