Law enforcement officials say the intense public interest and historic nature of the vote could lead to violent outbreaks if people are unhappy with the results, encounter problems casting their ballots or suspect voting irregularities.
Police departments say they cannot rule out disorder and are mobilising extra forces and putting SWAT teams on standby.
"This election is going to mark in history a change in the presidency: you're going to have a woman in the presidency or an African American as president. I think everybody around here is voting for Obama, so if he gets in the White House everybody's going to be happy.
He said Oakland was prepared to deal with unrest as Oakland Raiders fans rioted in 2003 following their Super Bowl loss.
Let's look at the psychology here:
People who riot for sports games are going to riot for elections too.
That sounds a lot like the meagre power of the basically powerless, doesn't it? First, a riot is usually nothing but destroying your own neighborhood; next, it looks like people are upset because the team they're cheering for didn't win.
That means they're not thinking about politics as changing the future. They're voting to get back at the other guy and feel a little better about how things suck.
That's not a healthy psychology by which to pick leaders -- or indeed, to decide anything.