The possible change, which could become law by Dec. 1, begins two months ahead of the New Hampshire primary. Nearly 20 Republicans and several Democrats are considering or running a bid for president. The huge field means the winner could claim victory with a small slice of support — so every vote counts.

New Hampshire lawmakers are poised to implement stricter guidelines on the state's same-day voter registration law by imposing a 30-day residency requirement. The measure has passed the state Senate and is now being vetted in the New Hampshire House.

CONCORD, N.H. — For the first time in more than two decades, presidential hopefuls seeking a vital win in New Hampshire's first-in-the-nation primary may lose out on motivating unregistered voters next year.


It's difficult to measure the impact of same-day voters on the primary or general election. But current and former strategists for presidential campaigns said same-day voters can add an element of the unexpected.

"Same-day is a challenge in that there can be surprises," said Jamie Burnett, political director for Mitt Romney's New Hampshire campaign in 2008. "It's generally a bigger challenge in general elections when you have massive turnouts."

Republican state Senator Sharon Carson said she filed the bill to prevent those who briefly reside in New Hampshire for work or other reasons to vote there out of convenience.

"Every time somebody fraudulently votes in New Hampshire, they take away someone else's vote," she said.

Carson noted that the state carries only four electoral votes in presidential elections, but they are considered precious because New Hampshire is a swing state.

House Minority Leader Steve Shurtleff said he sees no need for the bill and suggested it could take away someone's constitutional right if they decide to vote at the last minute.

"I think in some respects it's a solution looking for a problem," he said of the bill.


In a separate but related matter, the state Supreme Court is expected to decide by year's end whether a 2012 amendment to the same-day voter registration law is legal. A lawsuit brought on behalf of a group of University of New Hampshire students challenged the amendment, which required voters to claim residency in the state. Students had to register their cars or obtain a driver's license within 60 days of moving to the state to vote.

New Hampshire's same-day registration rules took effect in 1993, avoiding federal requirements set by the National Voter Registration Act, also known as the motor voter law. Under the law, people would not have to register to vote in their own city or town. They could also do so at Division of Motor Vehicles offices.

"The town clerks and people who do the voter registration in New Hampshire felt that it would add more security to the process if the local officials retained the authority like they have had for long, long, long time here rather than the provisions of the NVRA," said New Hampshire Secretary of State Bill Gardner.

Wayne Lesperance, a professor of political science at New England College, said same-day registration in New Hampshire has become a political football during the campaign season.

"The Democrats say the Republicans can't win on ideas, so they're restricting rights of people exercising their franchise," he said. "Republicans will say anecdotally we know voter fraud is going on."


Lesperance said there is no concrete data on the impact same-day registration.

"It may have far more impact on the politics of the election than the actual conduct of the election," he said.

New Hampshire is among 10 states in the nation with same-day voter registration.

Tom Rath, a longtime Republican political strategist, said he does not believe New Hampshire has significant voter fraud. But he said the state cannot detect whether out-of-state college students who claim residency elsewhere can vote in New Hampshire and their home state in the same election.

"We don't have any way to track that behavior," he said. "I think that's the bigger problem."

Political strategists warn New Hampshire voters are known for holding off on deciding which presidential candidate to support until just before polls open. Game-changing events can happen during the last hours of the New Hampshire primary, Gardner said.

"I could probably go back to every single primary where a candidate either benefited or was hurt by things that happened in those last few days," Gardner said. "People have no reason to lock themselves in. That's just the way it is here."

For Hillary Rodham Clinton, that moment happened on the eve of the New Hampshire primary in January 2008, when she teared up at a Portsmouth cafe. After that unexpected display of emotion in response to a simple question — "How do you do it?" — she won the primary, upending polls that showed Barack Obama in the lead. '


Lesperance said such moments can potentially inspire unregistered voters to the polls during a primary or general election.

"The pushback against that is that we should all be registering to vote," he said.

Rath, who is not affiliated with a campaign during this election cycle, said while there is no magic formula to win New Hampshire, local strategists know that even a half a percentage point can turn an election. And New Hampshire voters can jump into the race in unexpected ways. He cited a recent poll by WMUR that indicated that 40 percent of undeclared voters were going to take a Republican ballot in the upcoming primary.

"The idea is, in a close election, you want every possible advantage you can get," he said.