Could close race produce a popular/electoral vote split?

President Barack Obama and Republican challenger Mitt Romney are neck-and-neck in national polls, while Obama has an edge in crucial battleground states that will decide Tuesday's election.
The dynamic sets up a possible outcome that has happened rarely in American politics and could undermine the credibility of the victor -- Romney beats Obama in the overall vote, but the president gets reelected by winning the decisive Electoral College.
It would be the fifth time in history that the candidate who got the most overall support didn't win the...