Voters cast early ballots in California. Polls nationwide and in swing… (Mark Boster, Los Angeles…)
WASHINGTON — After a final cross-country campaign whirl by both candidates, President Obama heads into election day riding a slim lead in enough key states to secure a second term, while Mitt Romney remains competitive and could yet unseat him.
National polling showed late voter movement toward Obama, raising the possibility that the election might not drag out for days and weeks of wrangling over disputed ballots, as some feared. The president continued to maintain a slight edge in the vast majority of swing-state opinion polls, though his advantage typically remained within the surveys' margins of error, leaving the contest statistically tied.
An Obama reelection could shape a status-quo narrative of continued divided government in Washington. If Romney prevailed, 2012 would become the fourth national change election in a row, including the Democratic takeover of Congress in 2006, Obama's 2008 victory and the Republican return to power in the House in 2010.
INTERACTIVE: Predict a winner
"I actually think the question of this election comes down to this: Do you want four more years like the last four years. Or do you want real change?" Romney said Monday to chants of "Mitt! Mitt! Mitt!" at a rally in the northern Virginia suburbs outside Washington. The Republican asserted, as he has throughout a six-year quest for the presidency, that his record as a successful businessman, Winter Olympics chief and one-term governor of Massachusetts qualified him for the nation's highest office.
Obama answered back, telling supporters on what he said would be his last day as a candidate, "I know what real change looks like" and "We've got more change to make."
Tuesday's vote comes down to "a choice between returning to the top-down policies that crashed our economy, or a future that's built on providing opportunity to everybody and growing a strong middle class," the president said Monday in Madison, Wis.
Photos: America goes to the polls
More than 30 million Americans already have voted, and by the time all polling places close, more than 130 million Americans are expected to have cast ballots across the country. Most will be in places, including California, Illinois, Texas and New York, where the presidential election is not in doubt, because most states reliably favor the nominee of one major party or the other.
Insiders in both campaigns say they will be closely watching three states — Ohio, Wisconsin and Virginia — for clues to the outcome of the election.
On Monday, as the sun set on their prolonged and bitter campaign battle, Obama and Romney converged on Columbus, Ohio, a key swing area of the nation's most celebrated battleground state, which has gotten more candidate attention than any other.
Obama also campaigned in the heartland battlegrounds of Wisconsin and Iowa, and Romney stumped in Florida, Virginia and New Hampshire.
Romney has sought to add Pennsylvania to that mix, scheduling an election-day stop in Pittsburgh, along with another in Cleveland. Obama planned to spend the day in his hometown of Chicago, where he cast an early ballot last month.
Carrying Ohio — which Obama won four years ago — would open up a clear path to 270 electoral votes for the president. To win reelection, Obama would need to add only Wisconsin, assuming his advantage held in Nevada and other states regarded as likely to go Democratic. But Wisconsin, home to Republican vice presidential nominee Rep. Paul D. Ryan, is not a given. Recent polling shows Obama ahead by 3 or more percentage points, though a recent campaign poll had his lead down to a single percentage point (another had him ahead by 5).
If Obama loses Ohio, he'll need to make up the difference by carrying Colorado, Iowa and New Hampshire; late polling showed him with at least a marginal lead in all three. A Virginia win would give him breathing room and could be an early sign that he was headed for victory.
Romney's electoral math is more complicated, but almost certainly requires winning Ohio. A loss there would force him to pick up other states, including Wisconsin, Colorado and New Hampshire. He'd also have to carry Virginia and Florida, where the election could go either way.
Under the system laid out in the 1700s by the framers of the Constitution, a presidential election is actually a series of separate elections rather than a single national one. The 538 electoral votes that are up for grabs represent the sum of winner-take-all results in 48 states and the District of Columbia; also included are individual electoral votes from districts in Maine and Nebraska, which may differ from the statewide results under laws in those states. As recently as 2000, the winner of the nationwide popular vote — Al Gore — lost the electoral vote.
In the battlegrounds with the most electoral votes this time, demographics, local issues and competing voter turnout operations could make the difference. Here is a thumbnail look:
OHIO (18 electoral votes)