Democrat Barack Obama said months ago that he intended to compete hard in states that Democratic presidential nominees haven't won in decades.
He's done so well at expanding the battleground that a dozen states could claim bragging rights as most dramatic or decisive in the race between Obama and Republican John McCain.
Some states, such as Ohio, Florida and Missouri, are perpetually under the microscope on election nights because neither party can count on winning them.
Others, including typically Republican Virginia, North Carolina and Nevada, are new to the must-watch list, as polls show Obama leading or competitive.
Television networks won't project a winner in any state until polls there close. They also may be gun-shy about predicting winners based on surveys of voters leaving polling places, because such exit polls turned out to be inaccurate throughout most of Election Day in 2004. That means the networks may not call races until returns start to come in.
As vote tallies and analysis flood television networks and the Web, here's what to watch for tonight in four critical states. All times are Eastern.
7 p.m.: The New Old Dominion
Democrats have long been tempted by the changing demographics in Virginia, which last supported a Democratic nominee in 1964. Since Democrat John Kerry made a brief play for it in 2004, the state has moved from Republican red toward Democratic blue.
Democratic winners have included Gov. Tim Kaine in 2005 and Sen. Jim Webb in 2006.
In this year's Senate race between two former governors, polls show Democrat Mark Warner leading Republican Jim Gilmore by nearly 2 to 1.
Obama, ahead by single digits, made a massive investment in the state. He has three times as many field offices as McCain and last week spent about four times as much on TV ads ($2.5 million vs. $637,000, according to the Wisconsin Advertising Project).
On the final weekend, both men held rallies in the Washington suburbs of Northern Virginia. McCain is trying to stem the blue tide in the diverse, highly educated region that his brother, Joe, joked was "communist country."
Larry Sabato, head of the University of Virginia's Center for Politics, says Obama needs to win the region with 60% of the vote — about 7 points more than Kerry — to win the state.
Counties to watch: Bush won Prince William with 53% and Loudoun with 56%. Obama is looking to flip both and improve on Kerry's 53% in Fairfax County, the largest jurisdiction in the area, with 1 million residents.
Blacks, who made up about one-fifth of Virginia's electorate in 2004, gave Kerry 87% of their votes. Obama could do better. Keep an eye on returns and exit polls in Richmond and Virginia Beach tonight for clues.
McCain's strongholds include military voters around Norfolk and rural voters across southern Virginia. Obama needs to split the Norfolk region with McCain and hold at least 40% of the rural vote to win the state, Sabato says.
Late polls suggest Obama will hold all the states Kerry won and at least pick up Iowa. If that happens, and Obama also picks up Virginia's 13 electoral votes, McCain would have no mathematical path to victory.
"If Virginia goes for Obama, McCain's finished," Sabato says.
7:30 p.m.: Eye on the Buckeye
Ohio, with its 20 electoral votes, is center stage for the second election in a row. No Republican has won the presidency without taking Ohio since Abraham Lincoln did it in 1860.