Of all the messy outcomes, the one that seems likeliest is a candidate’s winning the presidency through the Electoral College despite losing the popular vote, as Mr. Bush did in 2000. If it happens again, it might be in the opposite way, with the Republican, Mr. Romney, in range of a popular plurality and the Democrat, Mr. Obama, with an apparently easier route to an Electoral College victory.
Charlie Cook, a well-known political handicapper, said the chance of that happening was 10 to 15 percent. Stanley B. Greenberg, a longtime Democratic pollster, put the odds at “one in three.”
“Not trivial,” Mr. Greenberg said of the chances. “If that happens, it is because the anti-Obama vote, mostly in the South, turns out in big numbers,” while the pro-Obama vote is not as overwhelming in Democratic states but pulls him over the top in vital places like Ohio, Iowa and Nevada.
If Mr. Obama wins a second term while losing the popular vote, it would again throw a harsh spotlight on the Electoral College, an artifact of the 18th century. Each state has one elector for each of its members in the House and Senate. With 538 electors, it takes 270 to win. If no one does, the House decides who will be president.
In 1800, Thomas Jefferson and Aaron Burr received the same number of electoral votes. The House sided with Jefferson. In 1824, none of four candidates received an electoral majority, and John Quincy Adams won in the House although he trailed Andrew Jackson in both the popular and the electoral votes.
Two other presidents, Rutherford B. Hayes in 1876 and Benjamin Harrison in 1888, won in the Electoral College even though they lost the popular vote.
The Electoral College has been attacked almost from the start. Over 200 years, more than 700 proposals to eliminate or revise it have been introduced in Congress, and more constitutional amendments have been proposed to change the system than on any other subject, according to the National Archives. A Gallup poll last year found that 62 percent favored a constitutional amendment making the popular vote decisive.
“If you were to have a repeat of that except the popular vote winner was the Republican and the Electoral College winner was the Democrat this time, then you would have had each party burned by the Electoral College over the course of 12 years, and that might be conducive to a serious look at reform,” said Robert W. Bennett, a Northwestern University law professor who has written extensively on the Electoral College.
Less likely is a tie, 269 to 269. If that happened, strategists envision an intense postelection campaign of state-by-state recounts, lawsuits, qualification challenges, efforts to flip electors, horse trading and pressure on members of Congress. The result would be a highly volatile 11-week obstacle course to Inauguration Day that would leave the country uncertain for a time about its next president and potentially undermine the credibility of the winner.
“If this election does require some extra innings, we have plans in place to deal with that,” said Bill Burton, a former Obama aide and co-founder of a super PAC supporting the president. “But the odds of that are infinitesimally small.”
If recounts did not change any Electoral College votes, both sides could lobby electors to switch before they met in state capitals on Dec. 17. While more than half the states have laws intended to force electors to cast ballots for the popular vote winner in their states, there have been “faithless electors.” In 2004, a Democratic elector in Minnesota wrote in John Edwards’s name instead of John Kerry’s.
If no electors flipped, the issue would go to the newly elected House. Each state gets one vote, meaning that Delaware has the same power as California. In the current House, Republicans control 33 delegations, while Democrats have 16 and 1 is split. Few analysts believe the election will change the House enough to shift that balance.
That would give Mr. Romney the advantage, although pressure would intensify if Mr. Obama won the popular vote. But even if Mr. Romney wins in the House, there is an extra wrinkle: The vice president would be chosen by the Senate, which may remain in Democratic hands.
If the Senate is deadlocked, the tie could be broken by Vice President Joseph R. Biden Jr., presumably voting for himself.
And the nation could wind up with President Romney and Vice President Biden.