The most expensive presidential race in American history now becomes the biggest show on television, a night with enough uncertainty that it could become a telethon lasting well into morning. For the third time in the last four presidential campaigns, the Democratic and Republican presidential nominees went into Election Day close in the national polls, with not one of the major opinion surveys giving President Obama or Mitt Romney a lead of statistical significance.
But presidential races are decided in the states, and the nation will get an answer to the opposing cases for victory that each candidate has made for so many months. It will finally know, as one of Mr. Obama’s top aides has put it, “which side is bluffing” and whether battleground-state polls, which have given Mr. Obama a slim but consistent edge where it matters most, accurately foretold the outcome. As the night unfolds, clues to the outcome will spill out well before the votes are counted.
If exit polling indicates that Mr. Romney is substantially exceeding the share of the white vote that went to Senator John McCain four years ago, that will be a sign that he is replicating the coalition that gave President George W. Bush a second term. If Mr. Obama can win Virginia, a battleground with an early poll-closing time, Mr. Romney’s options for getting an Electoral College majority will be substantially reduced. And in Ohio, the vote in Hamilton County, which Mr. Obama and Mr. Bush both won, could signal who takes the state.
On Monday, Mr. Romney and Mr. Obama went on traditional last-day blitzes across the most important swing states, overlapping in the place that is expected to have the lead role in Tuesday’s drama, Ohio.
For Mr. Obama, it was the last day of campaigning in a career that took him in a few short years from the Illinois State Senate to the United States Senate and, finally, the White House. For Mr. Romney, it was to be the end of his seven-year quest for the presidency. But late Monday, his aides announced that he would make one last pass at Pennsylvania and Ohio, with stops in Pittsburgh and Cleveland on Tuesday.
Some Republicans said they believed the final push was needed given that Mr. Romney was going into Election Day without any of the top competitive states definitively in his column. A senior party strategist lamented that for all the optimistic signs, there was a preponderance of evidence “cutting against us.”
Democrats will be on high alert on Tuesday for what they consider attempts to suppress the vote, while Republicans make a case that strict voter identification rules and counting procedures be followed to guarantee the integrity of the outcome. Batteries of lawyers are standing by for both sides in the swing states, especially Ohio, where the skirmishing was already under way.
The rise of early voting across the country meant that even before Election Day, more than 30 million Americans had cast their ballots. Those results will be reported Tuesday night, providing a new element for viewers at home: many states will report initial results that encompass far more votes than ever before.
Now, as the campaigns say, it is all about turnout. But beyond the cliché, the main question is not only how many but also who.
Mr. Romney’s campaign built its theory of winning around the idea that turnout for Mr. Obama will fall well below his 2008 tally. The Obama campaign did not entirely disagree, but believes it has rebuilt his coalition of women, Hispanics, blacks and young voters just enough to win.
Here is a guide to what to look for as the night progresses to know who is up, who is down and whether, should there be delayed counts, recounts and court challenges, Election Day becomes Election Week or — gasp! — Month. (All times below are Eastern.)
At 7 p.m., when the voting ends in Virginia, an early clue to whether the night will be a long one or a short one may emerge. Both sides pursued the state’s 13 electoral votes tenaciously, but they are more central to the strategy of Mr. Romney, who made two stops there on Monday.
If Mr. Obama carries Virginia, the path to victory narrows considerably for Mr. Romney, who will have to all but run the table of the remaining contested states. A senior adviser to the Romney campaign said the state’s importance is greater than its electoral votes because the outcome there could set the tone for the rest of election night.
At 7:30, the polls close in Ohio, where the 18 electoral votes are critical to both men. The county-by-county tallies will be carefully scrutinized when the returns start rolling in. But a word of warning: campaign officials do not expect an outcome for several hours — at the least. And if Mr. Obama appears to take a commanding lead right out of the gate, Republicans can take heart in the knowledge that the early vote — an expected Obama strength — is counted first, with the ballots from Election Day coming in later.
If Mr. Romney carries Ohio, viewers should settle in for a long night. A Romney victory there could signal that the vaunted ground organization of the Obama campaign is faltering and that his Midwestern firewall is cracking.
The television networks — and their high-tech maps — will spotlight the three C’s of Ohio: Cleveland, Columbus and Cincinnati. The president is looking for a strong performance in Cleveland, which Mr. Romney is visiting Tuesday in the hope of shaving down Democratic margins. And Republicans are looking for strength in Cincinnati and its surrounding area of Hamilton County; when Mr. Obama won the county in 2008, he was the first Democrat in a generation to do so.
But if Mr. Obama wins Ohio, history will be on his side (no Republican has won the White House without Ohio), as will the landscape of swing states. With Ohio in his column, he could lose Colorado, Virginia and Florida and still defeat Mr. Romney by 281 to 257 electoral votes.
At 8, the voting ends in Florida, New Hampshire and Pennsylvania. If the television networks are not able to call Pennsylvania quickly, Democrats have reason to move to the edge of their seats. But with 29 electoral votes, Florida is the biggest prize on the battleground map. The Obama campaign is not counting on victory there, but Mr. Romney needs to win. Otherwise, his advisers in Boston believe that Mr. Obama will be re-elected.
But keep this in mind about Florida: the ballot in many counties is unusually long, running more than 10 pages in some areas of the state because of judicial elections and initiatives, which means voting could take longer. And long lines in Florida could mean a long night ahead for Mr. Obama and Mr. Romney.
At 9, the voting ends in Colorado and Wisconsin. The states together have 19 electoral votes — one more than Ohio — and some strategists believe that the states could be split by Mr. Romney (Colorado) and Mr. Obama (Wisconsin). But if both states fall in one campaign’s favor, that candidate is almost certainly heading to the White House.
At 10, the polls close in Iowa. Both campaigns carefully courted the state, with its six electoral votes. The president selected Iowa as the site of his final rally on Monday night, a decision that his advisers said was rooted more in the symbolism of the place, where his victory in the 2008 caucuses solidified his rise on the national stage.
The result will answer the question of whether the visit to Des Moines was a moment of nostalgia or a last-minute scramble for support — or both.