WASHINGTON After billions of dollars, hours of debates and frantic last-minute pitches from the candidates, it's now up to the voters to decide whether to give President Barack Obama a second term or change course with Republican Mitt Romney.
Also at stake is control of Congress. Thirty-three Senate seats and all 435 House of Representatives seats are up this year, and while the House is expected to remain in Republican hands, Senate control hinges on a host of tight races.
Once the polls close starting at 3 p.m. PST in Indiana and Kentucky, a number of early clues will signal whether Obama or Romney will get the 270 electoral votes needed to win.
The first hints of how the night might go will come in four early poll-closing states: Virginia, North Carolina, New Hampshire and Indiana. Obama won all four in 2008.
Romney may need all four if he's to become the sixth person in 100 years to defeat a sitting president. Should he falter in even one, or the results become too close to call, this race won't be over quickly.
As the night unfolds, here's how to watch the returns:
Most states are solidly for Obama or Romney, so 11 are likely to decide the race. All have polling places scheduled to close by 7 p.m. PST. All went for Obama last time, and he has to hold most of them to win again.
4 p.m. PST: Virginia. Obama's 2008 victory was the first there by a Democratic presidential candidate since 1964. Romney needs its 13 electoral votes.
4:30 p.m. PST: Ohio, North Carolina. Romney needs Ohio and its 18 electoral votes; no Republican has won the White House without the state. North Carolina is another state Obama won in 2008, the first time a Democrat had taken it in decades, but Romney is counting on winning its 15 electoral votes. If not, he's probably in trouble.
5 p.m. PST: New Hampshire, Florida, Pennsylvania. If Obama wins Florida, Romney's chances get shakier. But if Romney wins Pennsylvania's 20 electoral votes, the president should start worrying. The four electoral votes of New Hampshire Democratic in the last two elections matter if the race stays close.
6 p.m. PST: Wisconsin, Colorado, Michigan. A Romney win in Michigan a state Obama won last time by 16 percentage points would be another sign that the president is faltering. Wisconsin and Colorado are tossups.
7 p.m. PST: Iowa, Nevada. Nevada has been trending Democratic. A strong Latino turnout would be a signal that Obama is doing well. Iowa is another tossup.
Turnout: Conventional wisdom says Democrats tend to dominate early voting, while Republicans do better on Election Day, so a big turnout could mean a big day for Romney.
Latino voting: Today marks the culmination of four years of registering new voters in hopes of harnessing growing Latino clout and shattering the reputation of Latinos as apathetic voters. In 2008, 50 percent of eligible Latino voters cast ballots, compared with 65 percent of blacks and 66 percent of whites, according to the Pew Hispanic Center. A big turnout could mean the difference in Colorado, Nevada and perhaps Arizona.
Hurricane Sandy: Will voters be more sympathetic to Obama in hard-hit states such as Pennsylvania or New Hampshire? Or blame the feds for being too slow to respond?
One of the night's more unpredictable cliffhangers involves control of the Senate. Democrats control 53 of the 100 seats, and they're defending 23 to the Republicans' 10.
Close races in Virginia, Indiana and Massachusetts might offer early hints as to whether Republicans can achieve the net gain of four three, if Romney is elected to win control. The next group of close races is farther west, notably in Wisconsin, Montana, Nevada and Arizona.
In the House, Democrats need a net gain of 25 for control, but independent analysts don't expect the party to gain more than 10.