Could Bernie Sanders' independent status shut him out of New Hampshire's Democratic primary?

From his run for mayor of Burlington to numerous campaigns for Congress, Vermont Sen. Bernie Sanders has for more than three decades eschewed traditional party labels in his pursuit of political office, winning election after election as an independent.

As he seeks the presidency as a Democrat, that unwillingness to be pigeonholed could be a liability in New Hampshire. To get on the ballot in the first-in-the-nation primary state, candidates must fill out paperwork that requires them to identify as a registered member of a political party.

"I don't know if it will be a problem," New Hampshire Secretary of State Bill Gardner said when asked whether Sanders' independent status could keep him off the ballot.

New Hampshire officials won't take up a case against Sanders without a complaint, Gardner said. A formal challenge to Sanders' eligibility would likely make its way to the state's Ballot Law Commission, the arbiter of such questions. Former Republican U.S. Rep. Charlie Bass raised the issue of Sanders' eligibility in a recent Washington Post opinion piece.

"In short, Sanders is not a Democrat, has not been elected as a Democrat, has never served as a Democrat and cannot plausibly claim, at least in New Hampshire, to be a Democrat," Bass wrote.

Sanders' campaign isn't worried.

"We think it will work out," Sanders' spokesman Michael Briggs told The Associated Press. "The senator has said that he'll do whatever it takes that he can do to qualify for the ballot."

Although New Hampshire's form asks candidates to declare their party registration, Vermont is one of a number of states where voters do not register with a party. Candidates, however, must consent to run in a specific party's primary, said Chris Winters, Vermont's deputy secretary of state.

In Sanders' 2006 and 2012 elections to the U.S. Senate, he consented to run in the Democratic primary. After getting the most votes in that contest, Sanders then rejected the nomination and ran as an independent in the general election, Winters said.

In the past, Sanders often has said he doesn't see enough daylight between Democrats and Republicans, arguing that both are too aligned with moneyed interests.

During an unsuccessful 1986 race for governor as an independent, Sanders said, "It is time to stop the Tweedledee, Tweedledum politics of the Republican and Democratic parties."

It's not as if his home-state Democrats are pining for a national party standard-bearer: Vermont Democrats including Gov. Peter Shumlin, former Gov. Howard Dean and Sen. Patrick Leahy are all backing former Secretary of State Hillary Rodham Clinton in the 2016 campaign.

In Congress, Sanders caucuses with Democrats and is the party's ranking member on the Senate Budget Committee. State and national Democratic officials don't think the paperwork question will affect Sanders.

"He is a Democratic candidate for president," said Ray Buckley, chairman of the New Hampshire Democratic Party. He said the state party would immediately go to court to have Sanders' name placed on the ballot if there is a challenge.

So far, other Democrats expected on the ballot are Clinton, former Rhode Island Gov. Lincoln Chafee, former Maryland Gov. Martin O'Malley and former U.S. Sen. Jim Webb of Virginia.

Clinton's campaign says it is prepared for a competitive primary and fully expects Sanders to be on the New Hampshire primary ballot.

Gardner, a staunch protector of the state's primary, said the wording about being registered in a party is included to help ensure integrity in elections. In New Hampshire, a voter must register with a particular party to vote in that party's primary.

"What applies to the voters, applies to the candidates," he said.

But, Gardner said, it's too early to speculate on Sanders' political fate.

"It's a whole series of hypotheticals," he said.