1. A surprising number of things could go wrong on Nov. 6. Though most are unlikely, anyone who remembers the 2000 election knows that's no guarantee. Here are five worst-case scenarios.
  2. An Electoral College tie

  3. (AP Photo/Pat Wellenbach)
  4. What's the scenario: Obama and Romney tie at 269 electors — one shy of the number needed to win the Electoral College. Under the the Constitution, the election is then thrown to the incoming members of the House. Each state delegation gets one vote. 
  5. Has it happened before: Yes. The House decided the elections of 1800 (Thomas Jefferson) and 1824 (John Quincy Adams).
  6. A faithless elector

  7. (AP Photo/Ben Margot)
  8. What's the scenario: Romney ekes out an Electoral College win over Obama, 270-268, but one or more Republican electors refuses to vote for him, likely by casting a protest vote for Rep. Ron Paul. The election is thrown to the House or Obama wins.
  9. Has it happened before: Surprisingly often. Among others, a 2004 Minnesota elector apparently accidentally voted for John Edwards, a 2000 D.C. elector refused to vote and a 1988 West Virginia elector voted for Lloyd Bentsen. 
  10. The winner loses the popular vote

  11. (AP Photo/Doug Mills)
  12. What's the scenario: One of the candidates wins the Electoral College while losing the national popular vote. If it's Romney, Democrats get really angry again. If it's Obama, Republicans rethink their support of the Electoral College.
  13. Has it happened before: Four times. Presidents who lost the popular vote include John Quincy Adams (1824), Rutherford B. Hayes (1876), Benjamin Harrison (1888) and George W. Bush (2000).
  14. A recount in a key state

  15. (AP Photo/J.Pat Carter)
  16. What's the scenario: The two candidates are so closely tied that the election hinges on a single state, where the vote is within the margin for a contentious and costly recount.
  17. Has it happened before: In 2000, the race between George W. Bush and Al Gore came down to Florida. Eventually, the U.S. Supreme Court stepped in and resolved the election by ending the recount.
  18. Who's worried about it: The New York Times' Nate Silver: "Another recount in Florida?" Huffington Post: "Republicans use $5.3 million recount fund to bolster total."