According to a Democratic National Committee aide, Sanders would not have a problem getting on Democratic primary and caucus ballots because the current party rules do not call for presidential candidates to be registered members of the party.
The DNC defines a presidential candidate as someone who "has accrued delegates in the nominating process and plans to seek the nomination, has established substantial support for his or her nomination as the Democratic candidate for the Office of the President of the United States, is a bona fide Democrat whose record of public service, accomplishment, public writings and/or public statements affirmatively demonstrates that he or she is faithful to the interests, welfare and success of the Democratic Party of the United States, and will participate in the Convention in good faith."
Sanders, according to the DNC aide who asked to be anonymous because he is not yet a candidate, appears to comply with those rules.
"There is no registration requirement," said the aide. "You have to be a good faith Democrats, but you don't have to submit some sort of proof of registration. There is no long form birth certificate required showing you were born a Democrat."
States do have the ability to write their own rules for who qualifies as a candidate in their respective primary or caucus, but the aide said no one at the DNC can recall a state that has ever included being a registered Democrat as a requirement for their presidential candidates.
That is the case for Iowa in 2016, too.
"The Iowa Democratic Party has always welcomed potential candidates for our party's Presidential nomination with open arms," said Christina Freundlich, spokeswoman for the Iowa Democratic Party. "In terms of who is eligible to participate as a candidate, we take our cues from the DNC's rules."
Tad Devine, a Democratic political consultant working with senator, points out that because Sanders has come up politically in Vermont -- a state with no party registration -- there is actually no way for him to register officially as a Democrat. "The mechanism doesn't exist," said Devine.
The political consultant, however, said that in order to get on the ballot in some states, Sanders would have to "pledge some allegiance to the Democratic Party."
"He won't have to sign on to every plank of the Democratic platform in order to get in, but he will have to acknowledge that he is running as a Democrat," Devine said. "I think Bernie will have to do that."
Sanders has caucused with the Democratic Party ever since he came to Washington as a congressman in 1991. He unsuccessfully ran for the United States Senate in 1971 as a member of Liberty Union party and, in 1981, when he successfully ran for mayor of Burlington, Vermont, he did so as an independent. At times, the senator identifies as a democratic (small D) socialist.
But now that he is considering a run for the Democratic nomination, his calculation is changing.
"I am getting balder and balder trying to figure these things out," he said at an event in Washington, D.C. on Monday where he acknowledged -- as he has before -- that he would not run outside the Democratic party establishment.
Whether he would change his party affiliation is another story.
"That is a decision I would have to make," he has said.
Devine, the political consultant working with Sanders, put it bluntly: "Would something stop Bernie from running as a Democrat? The bottom line answer to that is no."