Sen. Bernie Sanders (I-Vt.), who has never been elected to office as a Democrat, walked into the New Hampshire Secretary of State's Office on Thursday and declared himself a registered Democrat.

Sanders filed the formal paperwork Thursday afternoon to get his name on the ballot for the state's February 9 first-in-the-nation presidential primary. Sanders, hoping to stave off any challenges to his party status, was accompanied Thursday by a lawyer and Raymond Buckley, the New Hampshire Democratic Party chair, who had written a letter vouching that Sanders is — in the party's eyes — a Democrat.

Sanders handed Secretary of State Bill Gardner a check for $1,000 — the filing fee — assuring him it wouldn't bounce, according to WPTZ-TV.

It's unclear whether anyone will challenge Sanders' status as a registered Democrat. The New Hampshire form asks candidates to say, in part,  "I further declare that I am ... a registered member of the ___________________ party." Sanders wrote in the word "Democratic," campaign spokesman Karthik Ganapathy said.

The N.H. Secretary of State's Office appears unlikely to reject the form. "The filing will be accepted at face value," Dave Scanlan, a deputy secretary of state, told Seven Days. If someone else formally challenges Sanders' status, the matter would be decided by the Ballot Law Commission, he said.

Sanders, the longest serving independent in congressional history, has a long history as a maverick and has not won election to any office as a Democrat. But he has run in multiple Democratic primaries in Vermont, each time declining the nomination after he won it, to keep other candidates off the party's line in the general election.

Buckley, in an October 7 letter, noted that Sanders is on the ballot for the Democratic presidential primary in Vermont, has been invited to speak at the New Hampshire Democratic Party state convention and "supports the ideals of the New Hampshire Democratic Party."

Another wrinkle for any Vermonter declaring to be a registered Democrat: Vermont lacks party registration of any kind. That did not prevent former Vermont governor Howard Dean from getting his name on the presidential primary ballot in New Hampshire in 2004.

As he filed, Sanders also signed the secretary of state's candidate guest book. “We need a political revolution,” he wrote, according to his campaign. “Our government belongs to all of us, not just the 1 percent.”

As he was signing the book in front of news cameras, Sanders commented: "It doesn't look like something [Republican candidate Donald] Trump would say."