Picking the president isn't the only decision voters will have to make Tuesday. Voters in four deep blue states are also weighing in on marriage and how it should be defined.
In Washington, Minnesota, Maine, and Maryland, voters will decide on marriage and what kind of history they want to make.
If all four states vote for traditional marriage, they'll extend an unbroken record where voters in 32 states have supported the traditional institution.
In Washington, voters will decide whether to let stand a gay marriage law approved by lawmakers and the governor. Supporters of the law include major employers like Starbucks, Amazon, and Microsoft.
In Minnesota, the vote centers on a constitutional amendment that defines marriage as between one man and one woman.
In Maryland, voters will also consider a gay marriage law passed earlier this year. Traditional marriage strategist Frank Schubert, president of Mission: Public Affairs, said the black church could make the difference.
"A little over 20 percent of voters in Maryland are African-American and our opponents have really furiously gone after trying to conflict that vote," Schubert said.
In Maine, voters will sound off for the second time in three years. In 2009, they overturned a gay marriage bill passed by lawmakers. This year voters will decided whether to approve a new measure to legalize it.
In all four states traditional marriage forces face a fund-raising disadvantage. So far, they've raised just $12 million compared to $25 million on the gay marriage side.
For both camps the stakes are high. Not only do these votes matter for each state, they could affect the nation. Many believe the U.S. Supreme Court is watching, looking to see if the public has shifted.
"If the Supreme Court were to conclude that somehow the American people have changed and they now support same-sex marriage, it would make it easier for them to redefine marriage by judicial fiat," Schubert said.