Atlanta, Georgia (CNN) - Linda Underhill is one member of the largest voting bloc in New Hampshire: the independents.
More than 312,000 voters in the state are registered as "undeclared," as independents are called in the Granite State. Since August that voting group has seen its ranks grow slightly.
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Underhill, a resident of Merrimack, New Hampshire, has taken in several candidate events, including Mitt Romney's rally Saturday in Derry. After that appearance she told CNN she was leaning towards voting for Romney because she was impressed with his pitch.
Contacted Tuesday by CNN, she had changed her mind and had cast her vote for Jon Huntsman, who she called very smart and would likely aim for a bipartisan approach.
"In the past few days I watched him very closely," she said. "I just feel he is more genuine."
Underhill, who has voted for candidates of both parties and who did support candidate Barack Obama in 2008, watched both of this weekend's debates when Huntsman's performance had won some praise when he talked about why he had served as ambassador to China under a Democratic president because he wanted to serve the country.
Saying she now felt there was something "insincere" and "disingenuous" about Romney, she told CNN, "I can't get away from the fact that he is saying things that people want to hear."
The New Hampshire Secretary of State's office expects a record turnout in the GOP primary due in part to the participation of the "undeclared" voters. Since there is no competitive Democratic primary, unlike 2008, more of these voters are expected to vote in the Republican primary.
While these "undeclared" voters may be the largest single voting group, political experts in the state said it would be a mistake to think of them as one monolithic group.
Andrew Smith, a professor of political science at the University of New Hampshire and director of its polling center, said these voters should be seen in three distinct blocks: about 35% are really Democrats who mostly vote as Democrats; 30-35% align themselves mostly with Republicans and GOP candidates; and 30% are truly independent. Smith said these are the least likely to vote.
"What we are seeing in this election are about 60% who are going to vote are registered Republicans. Twenty percent are undeclared but who are really Republicans and behave like Republicans, 10% are undeclared who are Democrats...and 10% are true independent libertarians," Smith said.
For any campaign to be successful it has to understand these distinct voting groups and how to identify and reach them with the right message through phone calls, mailings and personal contacts.
"Talk about grassroots campaigning. That is true grassroots campaigning," Smith told CNN. That is "why Romney is in the best position. (His is the) only campaign that has that organization" to know which voters belong to which group and how to effectively sway them.
Smith and Dante Scala, also a political science professor at the University of New Hampshire, both said independents in the state are not the key to winning.
"It never determines the outcome of the election. You have to win with your registered party," Smith said. "The winning of the independents is icing on the cake."
Scala pointed to 2000 when Arizona Sen. John McCain did as well with GOP registered voters as opponent George W. Bush, but his support among the independents helped put him over the top.
Among independents, Huntsman and Romney were tied according to an American Research Group poll taken Jan. 8-9 with both getting 25% of that block and Ron Paul grabbing 20%.
Scala said with independents being such a large group, "it does provide some unpredictability especially for those true independents" because they may not be paying as much attention as others who have been following the campaign more closely.
"People with weaker attachment...could crash the party" this year and could help determine who comes in second, third or fourth place in this year's primary, because several candidates were bunched close together behind Romney, who has led all polls with a large margin.
In 2008, independents made up 37% of the primary electorate. John McCain got 40% of them while Romney garnered 27% of the group. About 75,000 of the GOP voters in 2008 were independent, while more than 121,000 of the Democratic voters belonged to that group.
– CNN Political Research Director Robert Yoon and CNN Political Producer Rachel Streitfeld contributed to this story.
Follow Kevin Bohn on Twitter @KevinBohnCNN.