Don't count on going to sleep tonight knowing who our next president is.
Given the razor-thin margins of national and battleground state polls, it's more than plausible that the vote counting continues until the wee hours — or later — in Ohio or another key state. (Florida?)
Remember, presidential elections are decided by the electoral vote, not the popular vote. And at least 40 states are so reliably Republican or Democratic that the campaigns largely ignore them and focus on the remaining states that swing both ways.
These are the states that will deliver Barack Obama or Mitt Romney to the 270 electoral-vote threshold it takes to win. Given the closeness of the polls, and the less-than-stellar track record of exit polls in recent elections, it's unlikely we'll see the networks call these states early.
With that in mind, here's your guide to watching election night results:
7 p.m. Polls close in all-important Virginia. If Romney loses Virginia's 13 electoral votes, his path to the White House is slim, but there's no telling how long before the state is called.
One county to watch? Loudoun. The upscale northern Virginia county exemplifies the changing demographics of Virginia, and Obama four years ago was the first Democrat to win it in 40 years. He doesn't have to win it again, but he needs to keep it competitive.
7:30 p.m. Polls close in Ohio and North Carolina. No state looms larger on this election than Ohio, with 18 electoral votes and where both campaigns have spent the most time. One county to watch: southwest Ohio's Hamilton County, home to Cincinnati and surrounding suburbs. Romney probably needs to carry Hamilton to carry the state, while Obama needs to keep it relatively close.
Ohio also offers a nightmare scenario if Obama and Romney virtually tie in the Buckeye State. Hundreds of thousands of voters in Ohio are likely to have to vote by provisional ballot, and state law gives local elections boards up to 10 days to determine the eligibility of provisional ballots. That could mean a serious delay in getting an Ohio winner if the vote is close.
North Carolina is another formerly solid red state that Romney needs to win. Keep an eye on Mecklenburg County, home to Charlotte, where Obama probably needs to pull at least 60 percent of the vote.
8 p.m. Polls close in Florida, New Hampshire and Pennsylvania. Actually, most polls in Florida close at 7 p.m., but results don't start getting posted until 8 p.m. because part of the Panhandle is in the Central Time Zone.
Florida is unpredictable, but simple: If Romney loses Florida, Obama wins a second term. Of course, the Sunshine State is hardly a model of smooth vote-counting, so don't bet on results coming quickly.
Florida counties to watch: Hillsborough, the state's best bellwether, and Orange and Miami-Dade. If Obama fails to win Orange and Miami-Dade by overwhelming margins, Florida will likely tip to Romney.
Most observers see Pennsylvania — which no Republican presidential candidate has won since 1988 — as a long shot for Romney, though he scheduled a last-minute trip to Pittsburgh today.
New Hampshire, with 4 electoral votes, has been leaning narrowly to Obama in recent polls.
9 p.m. Polls close in Colorado, Wisconsin, New Mexico, Michigan and Minnesota. Minnesota, Michigan and New Mexico look like safe states for Obama, but Wisconsin is competitive and Colorado looks dead even.
One county to keep an eye on in Colorado: Jefferson County outside of Denver, tends to swing both ways.
10 p.m. Polls close in Iowa, with six electoral votes, the last of the major battlegrounds to close its polls. The Obama campaign appears to have a comfortable cushion in early votes going into today, but independent voters have been moving to Romney.
Watch Polk County, home of Des Moines, where Obama probably needs to win by nearly 10 percentage points.
11 p.m. to ? Keep your fingers crossed.
Adam C. Smith can be reached at email@example.com.