Bernie Sanders rejected the nomination of the Democratic Party twice when he ran for the U.S. Senate in Vermont, choosing instead to remain the political independent he has been throughout his career.That could be a problem for him when he arrives in Secretary State Bill Gardner’s State House office later this year to register as a Democrat in the first-in-the-nation New Hampshire primary.Could Sanders actually be kept off of the ballot?Gardner, the state’s top election official for nearly 40 years, isn’t answering that question just yet. But he will make a judgment when the filing period opens, probably in October.New Hampshire’s official presidential primary “Declaration of Candidacy” form, governed by state law, requires a candidate to declare, “I am a registered member” of a political party.The problem is, Vermont, Sander’s home state, has no party registration. It’s an open system. Voters can vote in either a Republican or Democratic primary.Candidates run on either ballot, but not both.Gardner, after speaking with his counterpart in Vermont on Thursday evening, told WMUR.com that known Vermont Republicans have run in Democratic elections and Democrats have run as Republicans, entirely within Vermont law as an open state.Gardner said Vermont Secretary of State James Condos told him that Sanders was on Democratic primary ballots as a U.S. Senate candidate in 2006 and 2012 – and he won each of those primaries.In Vermont, party primary winners must either accept or reject the nominations of his or her party.Gardner said Condos confirmed that Sanders, after winning the Democratic primaries of 2006 and 2012, rejected the Democratic nomination and at the same time filed papers to be on the general election ballot as an independent -- and in each election, won.In the early 1970s, Sanders ran for governor and other offices as a member of the Vermont Labor Union Party. He resigned from that party in 1979. Sanders has never run in a general election as a Democrat.But Sanders long has been close to the Democratic Party. He has won the endorsements of top national Democrats in some of his elections. Even as an Independent he caucuses with the Democrats in the Senate. Earlier this year he was named by Senate Democratic Leader Harry Reid as the ranking member on the Senate Budget Committee.As of Thursday night, he was pictured at the top of the Democratic National Committee web site, next to a photo of Hillary Clinton.But when it comes to filing to appear on the New Hampshire primary ballot, none of that may matter. Here, it’s the state law that counts and the state law requires party registration. It's Gardner’s job to administer state election laws.Gardner is not jumping to any conclusions or prejudging Sanders’ eligibility.But he makes it clear: “At the time he files for the primary, he has got to be a registered member of a party. What he is right now is not going to be the deciding factor. It’s what he is at the time.”At that time, Gardner will decide whether Sanders is eligible. His decision may be challenged, and if so, he will issue a formal opinion.That opinion could be appealed to the state Ballot Law Commission, and possibly to the courts.Sanders’ team is unconcerned, at least outwardly.“Whatever we need to do to satisfy the requirement to get on the ballot in New Hampshire, or any other state, we will do,” said Sanders top adviser Tad Devine.Devine said that early Thursday, Sanders filed his campaign committee with the Federal Election Commission, and he stated his intention to seek the Democratic presidential nomination.Devine also pointed out that Vermont Gov. Howard Dean had no trouble getting on the 2004 New Hampshire primary ballot. And, he said, neither Texas nor Tennessee have party registration, yet George W. Bush and Al Gore also ran in the Granite State.Sanders’ situation is slightly different, and Gardner says it’s unique.Sanders rejected Democratic nominations, while Dean and Gore served as a governor and a U.S. senator, respectively, as Democrats, and Bush was a Republican governor.The state Democratic Party on Thursday night promised to help Sanders to get on the primary ballot."We welcome Senator Sanders to the New Hampshire presidential primary," said party chairman Raymond Buckley. "New Hampshire Democrats are excited to meet the candidates and hear about how we can build on the economic progress we’ve made over the past six years and continue to expand opportunities for New Hampshire’s middle class families."The New Hampshire Democratic Party will work to satisfy any concerns of the New Hampshire Secretary of State to ensure Sen. Sanders is on the democratic primary ballot," Buckley said.What will be the outcome of the Bernie Sanders eligibility question? That remains to be seen.But for now, chalk it up to still another fascinating moment in New Hampshire primary history.