Voters who are already in line when the polls close will still be allowed to vote. Obama's campaign is urging them not to give up -- and to get to the polls immediately if they are not already standing in line.

Obama even recorded a message just for his Twitter followers, exhorting them: "Guys, I'm serious. It's game time! Get out there. Go vote now."

Team Obama is also tweeting out messages specific to voters in Ohio, North Carolina, Pennsylvania, New Mexico, Wisconsin, Minnesota and Colorado, and had tweeted to Virginia voters before polls closed there. 

Early exit polls indicate the race between Obama and GOP nominee Mitt Romney is as close as it can get and will likely come down to voter turnout in key battleground states, which means Obama is counting on stalwart supporters to stay in line despite the dark and the cold. 

Polls have already closed in Virginia, Vermont, Georgia, Indiana, Kentucky, South Carolina, North Carolina, Ohio and West Virginia. Sixteen more states will close their polls at 8 p.m.