If you're eligible to vote but aren't registered yet, watch out. They're coming to get you!

Campaigns, political parties and interest groups are all mounting massive voter registration campaigns this year to influence the outcome of the November elections.

The target is the millions of Americans — the Pew Center on the States estimates that number is 51 million — who are eligible to vote but not registered. The belief is that even a relative few of these voters could swing the election results.

The NAACP says it plans to sign up 1.5 million new voters this year and will draw on a network of black churches, sororities and fraternities to help identify unregistered African-Americans.

At recent rallies for her husband, first lady Michelle Obama has encouraged students to make sure they re-register in the fall if they move over the summer.

And the Faith and Freedom Coalition has been working the crowds at NASCAR races in an effort to sign up 2 million new social conservatives. The Atlanta-based group is even sponsoring a race car with the words "Register to Vote" on the side.

The coalition's executive director, Gary Marx, says NASCAR fans tend to be conservative and they could make the difference in a close election.

"That margin could be sitting in the stands when there are over 100,000-plus screaming fans watching those cars rev around the track," he says.

Like other groups, the Faith and Freedom Coalition is using new techniques to identify which voters it wants to go after. It is using demographic and commercial information to build a database of millions of potential voters.

"We'll do things like look at who are the people that have maybe purchased a Bible in the last 18 to 24 months," says Marx. "It might be somebody that we would like to talk with about making sure they're registered to vote."

Especially, he says, if they live in crucial swing states, like Florida or Virginia.

Heather Smith, president of Rock the Vote, has her eyes on another group of voters. She says adults under 30 make up a quarter of the electorate, but are far less likely than older people to be registered. That's because young people tend to move around a lot. Many are also disillusioned with politics. She says 18 million people have also turned 18 since the last presidential election.

Rock the Vote hopes to use new technology to sign up 1.5 million young voters this year. It is offering an online registration system that makes it easy.

Smith says voters need only enter some basic information at the group's website, such as name, address and date of birth. "Then at the end, you're going to hit submit," she says. "And when you do, it produces a PDF of your voter registration form, completely filled out for you."

All the prospective voter has to do is print out the form, sign it and mail it in.

People can also use their smartphones to scan bar codes on Rock the Vote posters, concert tickets and other merchandise to access the registration form.

Rock the Vote will follow up with local election boards to make sure that the voters actually do get registered.

"It also allows us, as we get to Election Day, to send them a reminder that says, 'It's time to go vote. Here's where your polling place is. Here's what ID you need to bring,' " Smith says.

And there are other ambitious campaigns to sign up voters, including Hispanics, who are registered at lower rates than non-Hispanic blacks and whites.

Michael McDonald of George Mason University says registrations have generally been going up, but that the rolls need to be replenished because of the millions of voters who move.

"They're renters. They tend to be younger. They tend to be a little bit poorer. They tend to be a bit more minority," he says.

They also tend to vote Democratic, which is why one party is more actively registering than the other.

But McDonald says it's not enough just to get someone to fill out a form. It takes personal contact to make it matter in November.

That's one reason volunteers for President Obama's re-election campaign were at a Metro stop in Northern Virginia recently, registering the old-fashioned way. With clipboards in hand, cheerful volunteers asked everyone passing by if they were registered to vote yet.

It's a laborious process. Most of those asked were either from out of town, already registered or not interested.

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