Democratic presidential nominee Al Gore in 2000 won roughly 500,000 more votes than Republican nominee George W. Bush but lost the election.

In the next presidential race, Democratic challenger Sen. John Kerry lost to Bush by more than 3 million votes across all 50 states, but a mere 60,000 more votes in Ohio would have given him the election.

This year, some anticipate a similar scenario, where one candidate wins the popular vote and the other the Electoral College.

“The odds are always against it,” Larry Sabato, director of the University of Virginia’s Center for Politics, said. “But in a close election, it’s always possible. … It has happened four times in American history. Is it going to happen a fifth time this year? Nobody knows.”

With some national polls showing the possibility of Romney winning the popular vote over Obama but failing to secure 270 electoral votes, an effort is underway to eliminate the Electoral College.