Tuesday’s New Hampshire primary may be awarded in large part by voters who don't belong to either party.

The Granite State’s primary process allows independents to choose on Election Day which primary they want to vote in, which could complicate the strategy for campaigns and upend the current landscape that shows landslide wins on both sides of the aisle.

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Bernie Sanders currently leads Hillary Clinton by a double-digit margin in most Democratic polls in the state, while Donald Trump holds a commanding lead over the rest of the GOP field, where the next five candidates are caught in a logjam without much significant separation.

Many polls include independents leaning toward either party in samples, but the ultimate composition of who turns out for each primary is even harder to predict in New Hampshire than other states because of the independent element.

Political strategists estimate that independents make up an estimated 40 percent of the state’s electorate—so where they vote and how they vote could be crucial.

“There’s no question that the largest voting bloc in New Hampshire is independents,” Republican State Sen. Andy Sanborn said.

“There’s such a disappointment and frustration with both political parties on both sides, I think that’s going to bring a lot more independents out.”

Independents have played outsized roles in previous New Hampshire primaries, even if their picks don’t end up securing their party’s nomination. But their behavior is equally hard to predict before the primary.

Clinton came into the contest trailing Barack Obama in 2008, but flipped the script and won the state in large part because of success with independents.

And in 2000, John McCain edged out George W. Bush by 2 percent with Republican voters but by a whopping 43 points among independents in exit polls. That turned what could have been a narrow victory into an 18-point win in the state.

Few polls exist specifically analyzing Granite State independents—one reason why the state is so hard to predict.

A WBUR Radio poll conducted after the Feb. 1 Iowa caucuses showed that 49 percent of registered, undeclared voters leaned toward voting in the Republican primary, while 43 percent leaned toward the Democratic primary. The other 8 percent were undecided.

Those leaning toward the Democratic primary overwhelmingly support Bernie Sanders over Hillary Clinton, by a margin of 60 percent to 33 percent, according to the late-January version of that same poll. The February poll did not ask undeclared voters for specific candidate preference.

It’s a reality Sanders’ team is well aware of and is trumpeting as a sign of his electability.

“Being able to move independents into your party’s process and win a victory with their support is a critical test of general election strength,” Sanders strategist Tad Devine said.

“That’s a test we want to meet and master, and that’s the reason there’s so much of a premium placed on a victory in New Hampshire.”

Clinton’s team is well aware of the danger independents can be to her outcome in the state, said Michael Cuzzi, Barack Obama's 2008 deputy New Hampshire director.

“Based on polling, Clinton would rather see independent voters pulling a Republican ballot or staying home,” he said.

Her campaign is adopting the underdog theme in New Hampshire while looking to manage expectations, he said.

“If she’s 20 points down at the polls and pulls within 5 points of Sanders or brings it within single digits…she can play those expectations right and do another Clinton ‘Comeback Kid’ routine.”

While some believe that independents ultimately follow their voting histories and stay predominately loyal to one party, Cuzzi and others believe the large margin in the two-person Democratic race could dissuade independents from voting in that primary.

The GOP side could be more attractive, in part because of polarizing opinions about Donald Trump or the implications the vote has for the handful of establishment candidates all jockeying for supremacy.

“The perceived competitiveness of the race will be a factor, as a lot of these voters will want to go vote in a contest where they can have an impact,” Cuzzi said.

Fegus Cullen, a former state GOP chair who supports Ohio Gov. John Kasich, agrees.

“I’m inclined to think they go where the action is,” he said.

Recent polling of registered, undeclared voters largely reflects the general polling in the state—Donald Trump in first, followed by Ted Cruz in a distant second, narrowly edging out the cluster of establishment candidates.

The most recent poll from University of Massachusetts at Lowell, shows Trump leading independents with 34 percent, followed by Cruz’s 17 percent, Kasich’s 13 percent, and Rubio’s 12 percent. Chris Christie follows at 7 percent, with Bush just behind with 6 percent.

Kasich performs more than twice as well with independents as he does with registered Republican voters, with Christie the only other candidate polling better with that segment.

Kasich, Bush, Christie and Rubio aren’t surprising choices for independents—those candidates have sought to make inroads with the more moderate segments of the party.

But Sanborn, the GOP state senator, said Trump and Cruz resonate with independents because of their frustration with “establishment elitism” that wins out over a segment not rooted in partisan leanings.

Cuzzi, the former Obama staffer, estimated that between 25 percent and 45 percent of the state’s voters make up their minds within the last few days, while up to one-fifth don’t decide until primary day.

That underscores the importance of the final days before the race, which include debates well as a flurry of campaign appearances that could provide a last-minute nudge toward or away from a specific candidate.

Sanborn, who had previously endorsed Rand Paul but has not publicly endorsed a new candidate, noted Rick Santorum’s struggles to describe the record of newly-endorsed Marco Rubio as one potential event. Both Christie and Bush have jumped on that, releasing ads that include footage of that stumbling endorsement.

Ultimately, the independent element will likely make this New Hampshire primary as unpredictable as in previous years for both the Democrats and the Republicans. And while partisan voters will set the dynamics, the independents could be the ones to drive home a victory.

"The voting class is two mountaintops with a valley in the middle. You have people who are Democrats and lean Democrats...you've got hard Republicans and Republican [leaners]," Sanborn said.

"And then you have the middle--and those are the people who determine every single race."