MANCHESTER, N.H. – They say they're fed up with the partisan dysfunction in Washington – and their votes could be pivotal for Democratic hopefuls.

About 1,500 independent, moderate, and undeclared voters converged on the Problem Solver Convention on Sunday in Manchester, N.H. – with the first-in-the-nation primary a little over three months away.

About 42 percent – a plurality of New Hampshire voters – are registered as undeclared, according to the New Hampshire Secretary of State's voter rolls. Under the state's rules, undeclared voters can choose to vote in either party's primary – meaning there's a potential for a different kind of February surprise.

"There's really a silent majority of people out there who are not partisan and really are yearning for people in Washington to get together," said former Connecticut Sen. Joe Lieberman, who was a Democrat before becoming an independent during his last term in office. Lieberman, who helped organize the convention as chairman of the organization No Labels, said he is now a registered Democrat.

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In the 2016 campaign, President Trump gave a stump speech at the Problem Solver Convention. This cycle, presidential candidates Rep. Tulsi Gabbard, D-Hawaii, John Delaney, and Republican Bill Weld made their pitch to voters.

"Year after year, it gets worse and less gets done," Gabbard said of the partisan gridlock in D.C. "It's more about which party can angle the best to take back more seats in the next election."

Lieberman said as a registered Democrat, he's concerned about how the primary race has shifted the party further to the left – adding that the ongoing impeachment inquiry will only serve to intensify bitter political divisions.

"In the middle of an already partisan, divided, unproductive political system," Lieberman said, "it's only going to make it worse."

Moderate voters at the convention seemed to agree – pushing both parties to work together to find common ground.

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"It's extreme left on the Democratic side and extreme right on the Republican side," said Ken Tentarelli, a longtime independent voter from Newbury, N.H. "Unfortunately, the middle doesn't really have much of a voice."

Lieberman thinks the primary contest could change that.

"Independent voters are going to the [Democratic] primary," Lieberman said. "I think they're going to determine who wins."

But Professor Andrew Smith, a pollster at the University of New Hampshire Survey Center, doesn't think there really is such a thing as an independent voter in this hyperpartisan day in age.

"The truth is the independents in New Hampshire are a myth," Smith said. "There aren't anymore independent or independent-minded voters than there are in any other state in the country."

Indeed, the data shows that most undeclared do consistently vote either Republican or Democrat, Smith said.

"You can't rely on those undeclared or independent voters here to win the primary. Nobody's done that," Smith said. "Factions and parties want to motivate their bases in primaries."

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Come next November, none of the independent voters Fox News spoke to could see themselves voting for a third-party candidate.

"I'm not going to go for a third-party candidate," said New Hampshire moderate voter Frank Stama. "That's just the way to dilute your vote. You know, you're better off not voting than to dilute your vote."