Police departments countrywide think it's a possibility, and they're preparing for riots or other violent reactions to a McCain or Obama victory, The Hill reports.
There is particular concern that a loss by Obama, who has built a big lead in the polls, could prompt significant problems.
"Some worry that if Barack Obama loses and there is suspicion of foul play in the election, violence could ensue in cities with large black populations," The Hill writes. Detroit, Chicago, Oakland and Philadelphia are among the cities that plan to have extra police deployed.
"Are we anticipating it will be a riot situation? No. But will we be prepared if it goes awry? Yes," Oakland Police Department spokesman Jeff Thomason said.
Oakland will have extra units trained to deal with riots deployed and SWAT teams on standby when the results come in. Many police departments are preparing as they might for the possibility of a championship win or loss by a local sports team.
Some believe riots could come no matter who wins.
"If [Obama] is elected, like with sports championships, people may go out and riot," Bob Parks, an online columnist and black Republican candidate for state representative in Massachusetts, told The Hill. "If Barack Obama loses there will be another large group of people who will assume the election was stolen from him….. This will be an opportunity for people who want to commit mischief."